Merge branch 'release-v0.24.0' of github.com:matrix-org/synapse v0.24.0

83 files changed, 6538 insertions, 571 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index f1529e79bd..80518b7bae 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,3 +1,45 @@
+Changes in synapse v0.24.0 (2017-10-23)
+=======================================
+
+No changes since v0.24.0-rc1
+
+
+Changes in synapse v0.24.0-rc1 (2017-10-19)
+===========================================
+
+Features:
+
+* Add Group Server (PR #2352, #2363, #2374, #2377, #2378, #2382, #2410, #2426,
+  #2430, #2454, #2471, #2472, #2544)
+* Add support for channel notifications (PR #2501)
+* Add basic implementation of backup media store (PR #2538)
+* Add config option to auto-join new users to rooms (PR #2545)
+
+
+Changes:
+
+* Make the spam checker a module (PR #2474)
+* Delete expired url cache data (PR #2478)
+* Ignore incoming events for rooms that we have left (PR #2490)
+* Allow spam checker to reject invites too (PR #2492)
+* Add room creation checks to spam checker (PR #2495)
+* Spam checking: add the invitee to user_may_invite (PR #2502)
+* Process events from federation for different rooms in parallel (PR #2520)
+* Allow error strings from spam checker (PR #2531)
+* Improve error handling for missing files in config (PR #2551)
+
+
+Bug fixes:
+
+* Fix handling SERVFAILs when doing AAAA lookups for federation (PR #2477)
+* Fix incompatibility with newer versions of ujson (PR #2483) Thanks to
+  @jeremycline!
+* Fix notification keywords that start/end with non-word chars (PR #2500)
+* Fix stack overflow and logcontexts from linearizer (PR #2532)
+* Fix 500 error when fields missing from power_levels event (PR #2552)
+* Fix 500 error when we get an error handling a PDU (PR #2553)
+
+
 Changes in synapse v0.23.1 (2017-10-02)
 =======================================
 
diff --git a/docs/sphinx/conf.py b/docs/sphinx/conf.py
index 15c19834fc..0b15bd8912 100644
--- a/docs/sphinx/conf.py
+++ b/docs/sphinx/conf.py
@@ -50,7 +50,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = u'Synapse'
-copyright = u'2014, TNG'
+copyright = u'Copyright 2014-2017 OpenMarket Ltd, 2017 Vector Creations Ltd, 2017 New Vector Ltd'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
diff --git a/scripts/synapse_port_db b/scripts/synapse_port_db
index bc167b59af..dc7fe940e8 100755
--- a/scripts/synapse_port_db
+++ b/scripts/synapse_port_db
@@ -376,10 +376,13 @@ class Porter(object):
                         " VALUES (?,?,?,?,to_tsvector('english', ?),?,?)"
                     )
 
-                    rows_dict = [
-                        dict(zip(headers, row))
-                        for row in rows
-                    ]
+                    rows_dict = []
+                    for row in rows:
+                        d = dict(zip(headers, row))
+                        if "\0" in d['value']:
+                            logger.warn('dropping search row %s', d)
+                        else:
+                            rows_dict.append(d)
 
                     txn.executemany(sql, [
                         (
diff --git a/synapse/__init__.py b/synapse/__init__.py
index bee4aba625..c867d1cfd8 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -16,4 +16,4 @@
 """ This is a reference implementation of a Matrix home server.
 """
 
-__version__ = "0.23.1"
+__version__ = "0.24.0"
diff --git a/synapse/app/synchrotron.py b/synapse/app/synchrotron.py
index 80e4ba5336..576ac6fb7e 100644
--- a/synapse/app/synchrotron.py
+++ b/synapse/app/synchrotron.py
@@ -40,6 +40,7 @@ from synapse.replication.slave.storage.push_rule import SlavedPushRuleStore
 from synapse.replication.slave.storage.receipts import SlavedReceiptsStore
 from synapse.replication.slave.storage.registration import SlavedRegistrationStore
 from synapse.replication.slave.storage.room import RoomStore
+from synapse.replication.slave.storage.groups import SlavedGroupServerStore
 from synapse.replication.tcp.client import ReplicationClientHandler
 from synapse.rest.client.v1 import events
 from synapse.rest.client.v1.initial_sync import InitialSyncRestServlet
@@ -69,6 +70,7 @@ class SynchrotronSlavedStore(
     SlavedRegistrationStore,
     SlavedFilteringStore,
     SlavedPresenceStore,
+    SlavedGroupServerStore,
     SlavedDeviceInboxStore,
     SlavedDeviceStore,
     SlavedClientIpStore,
@@ -403,6 +405,10 @@ class SyncReplicationHandler(ReplicationClientHandler):
             )
         elif stream_name == "presence":
             yield self.presence_handler.process_replication_rows(token, rows)
+        elif stream_name == "receipts":
+            self.notifier.on_new_event(
+                "groups_key", token, users=[row.user_id for row in rows],
+            )
 
 
 def start(config_options):
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 1ab5593c6e..fa105bce72 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -82,21 +82,37 @@ class Config(object):
         return os.path.abspath(file_path) if file_path else file_path
 
     @classmethod
+    def path_exists(cls, file_path):
+        """Check if a file exists
+
+        Unlike os.path.exists, this throws an exception if there is an error
+        checking if the file exists (for example, if there is a perms error on
+        the parent dir).
+
+        Returns:
+            bool: True if the file exists; False if not.
+        """
+        try:
+            os.stat(file_path)
+            return True
+        except OSError as e:
+            if e.errno != errno.ENOENT:
+                raise e
+            return False
+
+    @classmethod
     def check_file(cls, file_path, config_name):
         if file_path is None:
             raise ConfigError(
                 "Missing config for %s."
-                " You must specify a path for the config file. You can "
-                "do this with the -c or --config-path option. "
-                "Adding --generate-config along with --server-name "
-                "<server name> will generate a config file at the given path."
                 % (config_name,)
             )
-        if not os.path.exists(file_path):
+        try:
+            os.stat(file_path)
+        except OSError as e:
             raise ConfigError(
-                "File %s config for %s doesn't exist."
-                " Try running again with --generate-config"
-                % (file_path, config_name,)
+                "Error accessing file '%s' (config for %s): %s"
+                % (file_path, config_name, e.strerror)
             )
         return cls.abspath(file_path)
 
@@ -248,7 +264,7 @@ class Config(object):
                     " -c CONFIG-FILE\""
                 )
             (config_path,) = config_files
-            if not os.path.exists(config_path):
+            if not cls.path_exists(config_path):
                 if config_args.keys_directory:
                     config_dir_path = config_args.keys_directory
                 else:
@@ -261,7 +277,7 @@ class Config(object):
                         "Must specify a server_name to a generate config for."
                         " Pass -H server.name."
                     )
-                if not os.path.exists(config_dir_path):
+                if not cls.path_exists(config_dir_path):
                     os.makedirs(config_dir_path)
                 with open(config_path, "wb") as config_file:
                     config_bytes, config = obj.generate_config(
diff --git a/synapse/config/groups.py b/synapse/config/groups.py
new file mode 100644
index 0000000000..997fa2881f
--- /dev/null
+++ b/synapse/config/groups.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ._base import Config
+
+
+class GroupsConfig(Config):
+    def read_config(self, config):
+        self.enable_group_creation = config.get("enable_group_creation", False)
+        self.group_creation_prefix = config.get("group_creation_prefix", "")
+
+    def default_config(self, **kwargs):
+        return """\
+        # Whether to allow non server admins to create groups on this server
+        enable_group_creation: false
+
+        # If enabled, non server admins can only create groups with local parts
+        # starting with this prefix
+        # group_creation_prefix: "unofficial/"
+        """
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index b22cacf8dc..05e242aef6 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -34,6 +34,8 @@ from .password_auth_providers import PasswordAuthProviderConfig
 from .emailconfig import EmailConfig
 from .workers import WorkerConfig
 from .push import PushConfig
+from .spam_checker import SpamCheckerConfig
+from .groups import GroupsConfig
 
 
 class HomeServerConfig(TlsConfig, ServerConfig, DatabaseConfig, LoggingConfig,
@@ -41,7 +43,8 @@ class HomeServerConfig(TlsConfig, ServerConfig, DatabaseConfig, LoggingConfig,
                        VoipConfig, RegistrationConfig, MetricsConfig, ApiConfig,
                        AppServiceConfig, KeyConfig, SAML2Config, CasConfig,
                        JWTConfig, PasswordConfig, EmailConfig,
-                       WorkerConfig, PasswordAuthProviderConfig, PushConfig,):
+                       WorkerConfig, PasswordAuthProviderConfig, PushConfig,
+                       SpamCheckerConfig, GroupsConfig,):
     pass
 
 
diff --git a/synapse/config/key.py b/synapse/config/key.py
index 6ee643793e..4b8fc063d0 100644
--- a/synapse/config/key.py
+++ b/synapse/config/key.py
@@ -118,10 +118,9 @@ class KeyConfig(Config):
         signing_keys = self.read_file(signing_key_path, "signing_key")
         try:
             return read_signing_keys(signing_keys.splitlines(True))
-        except Exception:
+        except Exception as e:
             raise ConfigError(
-                "Error reading signing_key."
-                " Try running again with --generate-config"
+                "Error reading signing_key: %s" % (str(e))
             )
 
     def read_old_signing_keys(self, old_signing_keys):
@@ -141,7 +140,8 @@ class KeyConfig(Config):
 
     def generate_files(self, config):
         signing_key_path = config["signing_key_path"]
-        if not os.path.exists(signing_key_path):
+
+        if not self.path_exists(signing_key_path):
             with open(signing_key_path, "w") as signing_key_file:
                 key_id = "a_" + random_string(4)
                 write_signing_keys(
diff --git a/synapse/config/password_auth_providers.py b/synapse/config/password_auth_providers.py
index 83762d089a..90824cab7f 100644
--- a/synapse/config/password_auth_providers.py
+++ b/synapse/config/password_auth_providers.py
@@ -15,13 +15,15 @@
 
 from ._base import Config, ConfigError
 
-import importlib
+from synapse.util.module_loader import load_module
 
 
 class PasswordAuthProviderConfig(Config):
     def read_config(self, config):
         self.password_providers = []
 
+        provider_config = None
+
         # We want to be backwards compatible with the old `ldap_config`
         # param.
         ldap_config = config.get("ldap_config", {})
@@ -38,19 +40,15 @@ class PasswordAuthProviderConfig(Config):
             if provider['module'] == "synapse.util.ldap_auth_provider.LdapAuthProvider":
                 from ldap_auth_provider import LdapAuthProvider
                 provider_class = LdapAuthProvider
+                try:
+                    provider_config = provider_class.parse_config(provider["config"])
+                except Exception as e:
+                    raise ConfigError(
+                        "Failed to parse config for %r: %r" % (provider['module'], e)
+                    )
             else:
-                # We need to import the module, and then pick the class out of
-                # that, so we split based on the last dot.
-                module, clz = provider['module'].rsplit(".", 1)
-                module = importlib.import_module(module)
-                provider_class = getattr(module, clz)
+                (provider_class, provider_config) = load_module(provider)
 
-            try:
-                provider_config = provider_class.parse_config(provider["config"])
-            except Exception as e:
-                raise ConfigError(
-                    "Failed to parse config for %r: %r" % (provider['module'], e)
-                )
             self.password_providers.append((provider_class, provider_config))
 
     def default_config(self, **kwargs):
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index f7e03c4cde..ef917fc9f2 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -41,6 +41,8 @@ class RegistrationConfig(Config):
             self.allow_guest_access and config.get("invite_3pid_guest", False)
         )
 
+        self.auto_join_rooms = config.get("auto_join_rooms", [])
+
     def default_config(self, **kwargs):
         registration_shared_secret = random_string_with_symbols(50)
 
@@ -70,6 +72,11 @@ class RegistrationConfig(Config):
             - matrix.org
             - vector.im
             - riot.im
+
+        # Users who register on this homeserver will automatically be joined
+        # to these rooms
+        #auto_join_rooms:
+        #    - "#example:example.com"
         """ % locals()
 
     def add_arguments(self, parser):
diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 2c6f57168e..6baa474931 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -70,7 +70,19 @@ class ContentRepositoryConfig(Config):
         self.max_upload_size = self.parse_size(config["max_upload_size"])
         self.max_image_pixels = self.parse_size(config["max_image_pixels"])
         self.max_spider_size = self.parse_size(config["max_spider_size"])
+
         self.media_store_path = self.ensure_directory(config["media_store_path"])
+
+        self.backup_media_store_path = config.get("backup_media_store_path")
+        if self.backup_media_store_path:
+            self.backup_media_store_path = self.ensure_directory(
+                self.backup_media_store_path
+            )
+
+        self.synchronous_backup_media_store = config.get(
+            "synchronous_backup_media_store", False
+        )
+
         self.uploads_path = self.ensure_directory(config["uploads_path"])
         self.dynamic_thumbnails = config["dynamic_thumbnails"]
         self.thumbnail_requirements = parse_thumbnail_requirements(
@@ -115,6 +127,14 @@ class ContentRepositoryConfig(Config):
         # Directory where uploaded images and attachments are stored.
         media_store_path: "%(media_store)s"
 
+        # A secondary directory where uploaded images and attachments are
+        # stored as a backup.
+        # backup_media_store_path: "%(media_store)s"
+
+        # Whether to wait for successful write to backup media store before
+        # returning successfully.
+        # synchronous_backup_media_store: false
+
         # Directory where in-progress uploads are stored.
         uploads_path: "%(uploads_path)s"
 
diff --git a/synapse/config/spam_checker.py b/synapse/config/spam_checker.py
new file mode 100644
index 0000000000..3fec42bdb0
--- /dev/null
+++ b/synapse/config/spam_checker.py
@@ -0,0 +1,35 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.util.module_loader import load_module
+
+from ._base import Config
+
+
+class SpamCheckerConfig(Config):
+    def read_config(self, config):
+        self.spam_checker = None
+
+        provider = config.get("spam_checker", None)
+        if provider is not None:
+            self.spam_checker = load_module(provider)
+
+    def default_config(self, **kwargs):
+        return """\
+        # spam_checker:
+        #     module: "my_custom_project.SuperSpamChecker"
+        #     config:
+        #         example_option: 'things'
+        """
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index e081840a83..247f18f454 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -126,7 +126,7 @@ class TlsConfig(Config):
         tls_private_key_path = config["tls_private_key_path"]
         tls_dh_params_path = config["tls_dh_params_path"]
 
-        if not os.path.exists(tls_private_key_path):
+        if not self.path_exists(tls_private_key_path):
             with open(tls_private_key_path, "w") as private_key_file:
                 tls_private_key = crypto.PKey()
                 tls_private_key.generate_key(crypto.TYPE_RSA, 2048)
@@ -141,7 +141,7 @@ class TlsConfig(Config):
                     crypto.FILETYPE_PEM, private_key_pem
                 )
 
-        if not os.path.exists(tls_certificate_path):
+        if not self.path_exists(tls_certificate_path):
             with open(tls_certificate_path, "w") as certificate_file:
                 cert = crypto.X509()
                 subject = cert.get_subject()
@@ -159,7 +159,7 @@ class TlsConfig(Config):
 
                 certificate_file.write(cert_pem)
 
-        if not os.path.exists(tls_dh_params_path):
+        if not self.path_exists(tls_dh_params_path):
             if GENERATE_DH_PARAMS:
                 subprocess.check_call([
                     "openssl", "dhparam",
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 4096c606f1..9e746a28bf 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -470,14 +470,14 @@ def _check_power_levels(event, auth_events):
         ("invite", None),
     ]
 
-    old_list = current_state.content.get("users")
+    old_list = current_state.content.get("users", {})
     for user in set(old_list.keys() + user_list.keys()):
         levels_to_check.append(
             (user, "users")
         )
 
-    old_list = current_state.content.get("events")
-    new_list = event.content.get("events")
+    old_list = current_state.content.get("events", {})
+    new_list = event.content.get("events", {})
     for ev_id in set(old_list.keys() + new_list.keys()):
         levels_to_check.append(
             (ev_id, "events")
diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index 56fa9e556e..dccc579eac 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -14,25 +14,100 @@
 # limitations under the License.
 
 
-def check_event_for_spam(event):
-    """Checks if a given event is considered "spammy" by this server.
+class SpamChecker(object):
+    def __init__(self, hs):
+        self.spam_checker = None
 
-    If the server considers an event spammy, then it will be rejected if
-    sent by a local user. If it is sent by a user on another server, then
-    users receive a blank event.
+        module = None
+        config = None
+        try:
+            module, config = hs.config.spam_checker
+        except:
+            pass
 
-    Args:
-        event (synapse.events.EventBase): the event to be checked
+        if module is not None:
+            self.spam_checker = module(config=config)
 
-    Returns:
-        bool: True if the event is spammy.
-    """
-    if not hasattr(event, "content") or "body" not in event.content:
-        return False
+    def check_event_for_spam(self, event):
+        """Checks if a given event is considered "spammy" by this server.
 
-    # for example:
-    #
-    # if "the third flower is green" in event.content["body"]:
-    #    return True
+        If the server considers an event spammy, then it will be rejected if
+        sent by a local user. If it is sent by a user on another server, then
+        users receive a blank event.
 
-    return False
+        Args:
+            event (synapse.events.EventBase): the event to be checked
+
+        Returns:
+            bool: True if the event is spammy.
+        """
+        if self.spam_checker is None:
+            return False
+
+        return self.spam_checker.check_event_for_spam(event)
+
+    def user_may_invite(self, inviter_userid, invitee_userid, room_id):
+        """Checks if a given user may send an invite
+
+        If this method returns false, the invite will be rejected.
+
+        Args:
+            userid (string): The sender's user ID
+
+        Returns:
+            bool: True if the user may send an invite, otherwise False
+        """
+        if self.spam_checker is None:
+            return True
+
+        return self.spam_checker.user_may_invite(inviter_userid, invitee_userid, room_id)
+
+    def user_may_create_room(self, userid):
+        """Checks if a given user may create a room
+
+        If this method returns false, the creation request will be rejected.
+
+        Args:
+            userid (string): The sender's user ID
+
+        Returns:
+            bool: True if the user may create a room, otherwise False
+        """
+        if self.spam_checker is None:
+            return True
+
+        return self.spam_checker.user_may_create_room(userid)
+
+    def user_may_create_room_alias(self, userid, room_alias):
+        """Checks if a given user may create a room alias
+
+        If this method returns false, the association request will be rejected.
+
+        Args:
+            userid (string): The sender's user ID
+            room_alias (string): The alias to be created
+
+        Returns:
+            bool: True if the user may create a room alias, otherwise False
+        """
+        if self.spam_checker is None:
+            return True
+
+        return self.spam_checker.user_may_create_room_alias(userid, room_alias)
+
+    def user_may_publish_room(self, userid, room_id):
+        """Checks if a given user may publish a room to the directory
+
+        If this method returns false, the publish request will be rejected.
+
+        Args:
+            userid (string): The sender's user ID
+            room_id (string): The ID of the room that would be published
+
+        Returns:
+            bool: True if the user may publish the room, otherwise False
+        """
+        if self.spam_checker is None:
+            return True
+
+        return self.spam_checker.user_may_publish_room(userid, room_id)
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index babd9ea078..a0f5d40eb3 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -16,7 +16,6 @@ import logging
 
 from synapse.api.errors import SynapseError
 from synapse.crypto.event_signing import check_event_content_hash
-from synapse.events import spamcheck
 from synapse.events.utils import prune_event
 from synapse.util import unwrapFirstError, logcontext
 from twisted.internet import defer
@@ -26,7 +25,7 @@ logger = logging.getLogger(__name__)
 
 class FederationBase(object):
     def __init__(self, hs):
-        pass
+        self.spam_checker = hs.get_spam_checker()
 
     @defer.inlineCallbacks
     def _check_sigs_and_hash_and_fetch(self, origin, pdus, outlier=False,
@@ -144,7 +143,7 @@ class FederationBase(object):
                     )
                     return redacted
 
-                if spamcheck.check_event_for_spam(pdu):
+                if self.spam_checker.check_event_for_spam(pdu):
                     logger.warn(
                         "Event contains spam, redacting %s: %s",
                         pdu.event_id, pdu.get_pdu_json()
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 51e3fdea06..e15228e70b 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -12,14 +12,12 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
-
 from twisted.internet import defer
 
 from .federation_base import FederationBase
 from .units import Transaction, Edu
 
-from synapse.util.async import Linearizer
+from synapse.util import async
 from synapse.util.logutils import log_function
 from synapse.util.caches.response_cache import ResponseCache
 from synapse.events import FrozenEvent
@@ -33,6 +31,9 @@ from synapse.crypto.event_signing import compute_event_signature
 import simplejson as json
 import logging
 
+# when processing incoming transactions, we try to handle multiple rooms in
+# parallel, up to this limit.
+TRANSACTION_CONCURRENCY_LIMIT = 10
 
 logger = logging.getLogger(__name__)
 
@@ -52,7 +53,8 @@ class FederationServer(FederationBase):
 
         self.auth = hs.get_auth()
 
-        self._server_linearizer = Linearizer("fed_server")
+        self._server_linearizer = async.Linearizer("fed_server")
+        self._transaction_linearizer = async.Linearizer("fed_txn_handler")
 
         # We cache responses to state queries, as they take a while and often
         # come in waves.
@@ -109,25 +111,41 @@ class FederationServer(FederationBase):
     @defer.inlineCallbacks
     @log_function
     def on_incoming_transaction(self, transaction_data):
+        # keep this as early as possible to make the calculated origin ts as
+        # accurate as possible.
+        request_time = self._clock.time_msec()
+
         transaction = Transaction(**transaction_data)
 
-        received_pdus_counter.inc_by(len(transaction.pdus))
+        if not transaction.transaction_id:
+            raise Exception("Transaction missing transaction_id")
+        if not transaction.origin:
+            raise Exception("Transaction missing origin")
 
-        for p in transaction.pdus:
-            if "unsigned" in p:
-                unsigned = p["unsigned"]
-                if "age" in unsigned:
-                    p["age"] = unsigned["age"]
-            if "age" in p:
-                p["age_ts"] = int(self._clock.time_msec()) - int(p["age"])
-                del p["age"]
+        logger.debug("[%s] Got transaction", transaction.transaction_id)
 
-        pdu_list = [
-            self.event_from_pdu_json(p) for p in transaction.pdus
-        ]
+        # use a linearizer to ensure that we don't process the same transaction
+        # multiple times in parallel.
+        with (yield self._transaction_linearizer.queue(
+                (transaction.origin, transaction.transaction_id),
+        )):
+            result = yield self._handle_incoming_transaction(
+                transaction, request_time,
+            )
 
-        logger.debug("[%s] Got transaction", transaction.transaction_id)
+        defer.returnValue(result)
+
+    @defer.inlineCallbacks
+    def _handle_incoming_transaction(self, transaction, request_time):
+        """ Process an incoming transaction and return the HTTP response
+
+        Args:
+            transaction (Transaction): incoming transaction
+            request_time (int): timestamp that the HTTP request arrived at
 
+        Returns:
+            Deferred[(int, object)]: http response code and body
+        """
         response = yield self.transaction_actions.have_responded(transaction)
 
         if response:
@@ -140,42 +158,49 @@ class FederationServer(FederationBase):
 
         logger.debug("[%s] Transaction is new", transaction.transaction_id)
 
-        results = []
-
-        for pdu in pdu_list:
-            # check that it's actually being sent from a valid destination to
-            # workaround bug #1753 in 0.18.5 and 0.18.6
-            if transaction.origin != get_domain_from_id(pdu.event_id):
-                # We continue to accept join events from any server; this is
-                # necessary for the federation join dance to work correctly.
-                # (When we join over federation, the "helper" server is
-                # responsible for sending out the join event, rather than the
-                # origin. See bug #1893).
-                if not (
-                    pdu.type == 'm.room.member' and
-                    pdu.content and
-                    pdu.content.get("membership", None) == 'join'
-                ):
-                    logger.info(
-                        "Discarding PDU %s from invalid origin %s",
-                        pdu.event_id, transaction.origin
-                    )
-                    continue
-                else:
-                    logger.info(
-                        "Accepting join PDU %s from %s",
-                        pdu.event_id, transaction.origin
-                    )
+        received_pdus_counter.inc_by(len(transaction.pdus))
 
-            try:
-                yield self._handle_received_pdu(transaction.origin, pdu)
-                results.append({})
-            except FederationError as e:
-                self.send_failure(e, transaction.origin)
-                results.append({"error": str(e)})
-            except Exception as e:
-                results.append({"error": str(e)})
-                logger.exception("Failed to handle PDU")
+        pdus_by_room = {}
+
+        for p in transaction.pdus:
+            if "unsigned" in p:
+                unsigned = p["unsigned"]
+                if "age" in unsigned:
+                    p["age"] = unsigned["age"]
+            if "age" in p:
+                p["age_ts"] = request_time - int(p["age"])
+                del p["age"]
+
+            event = self.event_from_pdu_json(p)
+            room_id = event.room_id
+            pdus_by_room.setdefault(room_id, []).append(event)
+
+        pdu_results = {}
+
+        # we can process different rooms in parallel (which is useful if they
+        # require callouts to other servers to fetch missing events), but
+        # impose a limit to avoid going too crazy with ram/cpu.
+        @defer.inlineCallbacks
+        def process_pdus_for_room(room_id):
+            logger.debug("Processing PDUs for %s", room_id)
+            for pdu in pdus_by_room[room_id]:
+                event_id = pdu.event_id
+                try:
+                    yield self._handle_received_pdu(
+                        transaction.origin, pdu
+                    )
+                    pdu_results[event_id] = {}
+                except FederationError as e:
+                    logger.warn("Error handling PDU %s: %s", event_id, e)
+                    pdu_results[event_id] = {"error": str(e)}
+                except Exception as e:
+                    pdu_results[event_id] = {"error": str(e)}
+                    logger.exception("Failed to handle PDU %s", event_id)
+
+        yield async.concurrently_execute(
+            process_pdus_for_room, pdus_by_room.keys(),
+            TRANSACTION_CONCURRENCY_LIMIT,
+        )
 
         if hasattr(transaction, "edus"):
             for edu in (Edu(**x) for x in transaction.edus):
@@ -185,17 +210,16 @@ class FederationServer(FederationBase):
                     edu.content
                 )
 
-            for failure in getattr(transaction, "pdu_failures", []):
-                logger.info("Got failure %r", failure)
-
-        logger.debug("Returning: %s", str(results))
+        pdu_failures = getattr(transaction, "pdu_failures", [])
+        for failure in pdu_failures:
+            logger.info("Got failure %r", failure)
 
         response = {
-            "pdus": dict(zip(
-                (p.event_id for p in pdu_list), results
-            )),
+            "pdus": pdu_results,
         }
 
+        logger.debug("Returning: %s", str(response))
+
         yield self.transaction_actions.set_response(
             transaction,
             200, response
@@ -520,6 +544,30 @@ class FederationServer(FederationBase):
         Returns (Deferred): completes with None
         Raises: FederationError if the signatures / hash do not match
     """
+        # check that it's actually being sent from a valid destination to
+        # workaround bug #1753 in 0.18.5 and 0.18.6
+        if origin != get_domain_from_id(pdu.event_id):
+            # We continue to accept join events from any server; this is
+            # necessary for the federation join dance to work correctly.
+            # (When we join over federation, the "helper" server is
+            # responsible for sending out the join event, rather than the
+            # origin. See bug #1893).
+            if not (
+                pdu.type == 'm.room.member' and
+                pdu.content and
+                pdu.content.get("membership", None) == 'join'
+            ):
+                logger.info(
+                    "Discarding PDU %s from invalid origin %s",
+                    pdu.event_id, origin
+                )
+                return
+            else:
+                logger.info(
+                    "Accepting join PDU %s from %s",
+                    pdu.event_id, origin
+                )
+
         # Check signature.
         try:
             pdu = yield self._check_sigs_and_hash(pdu)
diff --git a/synapse/federation/transaction_queue.py b/synapse/federation/transaction_queue.py
index 003eaba893..7a3c9cbb70 100644
--- a/synapse/federation/transaction_queue.py
+++ b/synapse/federation/transaction_queue.py
@@ -20,8 +20,8 @@ from .persistence import TransactionActions
 from .units import Transaction, Edu
 
 from synapse.api.errors import HttpResponseException
+from synapse.util import logcontext
 from synapse.util.async import run_on_reactor
-from synapse.util.logcontext import preserve_context_over_fn, preserve_fn
 from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
 from synapse.util.metrics import measure_func
 from synapse.handlers.presence import format_user_presence_state, get_interested_remotes
@@ -231,11 +231,9 @@ class TransactionQueue(object):
                 (pdu, order)
             )
 
-            preserve_context_over_fn(
-                self._attempt_new_transaction, destination
-            )
+            self._attempt_new_transaction(destination)
 
-    @preserve_fn  # the caller should not yield on this
+    @logcontext.preserve_fn  # the caller should not yield on this
     @defer.inlineCallbacks
     def send_presence(self, states):
         """Send the new presence states to the appropriate destinations.
@@ -299,7 +297,7 @@ class TransactionQueue(object):
                     state.user_id: state for state in states
                 })
 
-                preserve_fn(self._attempt_new_transaction)(destination)
+                self._attempt_new_transaction(destination)
 
     def send_edu(self, destination, edu_type, content, key=None):
         edu = Edu(
@@ -321,9 +319,7 @@ class TransactionQueue(object):
         else:
             self.pending_edus_by_dest.setdefault(destination, []).append(edu)
 
-        preserve_context_over_fn(
-            self._attempt_new_transaction, destination
-        )
+        self._attempt_new_transaction(destination)
 
     def send_failure(self, failure, destination):
         if destination == self.server_name or destination == "localhost":
@@ -336,9 +332,7 @@ class TransactionQueue(object):
             destination, []
         ).append(failure)
 
-        preserve_context_over_fn(
-            self._attempt_new_transaction, destination
-        )
+        self._attempt_new_transaction(destination)
 
     def send_device_messages(self, destination):
         if destination == self.server_name or destination == "localhost":
@@ -347,15 +341,24 @@ class TransactionQueue(object):
         if not self.can_send_to(destination):
             return
 
-        preserve_context_over_fn(
-            self._attempt_new_transaction, destination
-        )
+        self._attempt_new_transaction(destination)
 
     def get_current_token(self):
         return 0
 
-    @defer.inlineCallbacks
     def _attempt_new_transaction(self, destination):
+        """Try to start a new transaction to this destination
+
+        If there is already a transaction in progress to this destination,
+        returns immediately. Otherwise kicks off the process of sending a
+        transaction in the background.
+
+        Args:
+            destination (str):
+
+        Returns:
+            None
+        """
         # list of (pending_pdu, deferred, order)
         if destination in self.pending_transactions:
             # XXX: pending_transactions can get stuck on by a never-ending
@@ -368,6 +371,19 @@ class TransactionQueue(object):
             )
             return
 
+        logger.debug("TX [%s] Starting transaction loop", destination)
+
+        # Drop the logcontext before starting the transaction. It doesn't
+        # really make sense to log all the outbound transactions against
+        # whatever path led us to this point: that's pretty arbitrary really.
+        #
+        # (this also means we can fire off _perform_transaction without
+        # yielding)
+        with logcontext.PreserveLoggingContext():
+            self._transaction_transmission_loop(destination)
+
+    @defer.inlineCallbacks
+    def _transaction_transmission_loop(self, destination):
         pending_pdus = []
         try:
             self.pending_transactions[destination] = 1
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 52b2a717d2..125d8f3598 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -471,3 +471,384 @@ class TransportLayerClient(object):
         )
 
         defer.returnValue(content)
+
+    @log_function
+    def get_group_profile(self, destination, group_id, requester_user_id):
+        """Get a group profile
+        """
+        path = PREFIX + "/groups/%s/profile" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_group_summary(self, destination, group_id, requester_user_id):
+        """Get a group summary
+        """
+        path = PREFIX + "/groups/%s/summary" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_rooms_in_group(self, destination, group_id, requester_user_id):
+        """Get all rooms in a group
+        """
+        path = PREFIX + "/groups/%s/rooms" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    def add_room_to_group(self, destination, group_id, requester_user_id, room_id,
+                          content):
+        """Add a room to a group
+        """
+        path = PREFIX + "/groups/%s/room/%s" % (group_id, room_id,)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    def remove_room_from_group(self, destination, group_id, requester_user_id, room_id):
+        """Remove a room from a group
+        """
+        path = PREFIX + "/groups/%s/room/%s" % (group_id, room_id,)
+
+        return self.client.delete_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_users_in_group(self, destination, group_id, requester_user_id):
+        """Get users in a group
+        """
+        path = PREFIX + "/groups/%s/users" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_invited_users_in_group(self, destination, group_id, requester_user_id):
+        """Get users that have been invited to a group
+        """
+        path = PREFIX + "/groups/%s/invited_users" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def accept_group_invite(self, destination, group_id, user_id, content):
+        """Accept a group invite
+        """
+        path = PREFIX + "/groups/%s/users/%s/accept_invite" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def invite_to_group(self, destination, group_id, user_id, requester_user_id, content):
+        """Invite a user to a group
+        """
+        path = PREFIX + "/groups/%s/users/%s/invite" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def invite_to_group_notification(self, destination, group_id, user_id, content):
+        """Sent by group server to inform a user's server that they have been
+        invited.
+        """
+
+        path = PREFIX + "/groups/local/%s/users/%s/invite" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def remove_user_from_group(self, destination, group_id, requester_user_id,
+                               user_id, content):
+        """Remove a user fron a group
+        """
+        path = PREFIX + "/groups/%s/users/%s/remove" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def remove_user_from_group_notification(self, destination, group_id, user_id,
+                                            content):
+        """Sent by group server to inform a user's server that they have been
+        kicked from the group.
+        """
+
+        path = PREFIX + "/groups/local/%s/users/%s/remove" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def renew_group_attestation(self, destination, group_id, user_id, content):
+        """Sent by either a group server or a user's server to periodically update
+        the attestations
+        """
+
+        path = PREFIX + "/groups/%s/renew_attestation/%s" % (group_id, user_id)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def update_group_summary_room(self, destination, group_id, user_id, room_id,
+                                  category_id, content):
+        """Update a room entry in a group summary
+        """
+        if category_id:
+            path = PREFIX + "/groups/%s/summary/categories/%s/rooms/%s" % (
+                group_id, category_id, room_id,
+            )
+        else:
+            path = PREFIX + "/groups/%s/summary/rooms/%s" % (group_id, room_id,)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def delete_group_summary_room(self, destination, group_id, user_id, room_id,
+                                  category_id):
+        """Delete a room entry in a group summary
+        """
+        if category_id:
+            path = PREFIX + "/groups/%s/summary/categories/%s/rooms/%s" % (
+                group_id, category_id, room_id,
+            )
+        else:
+            path = PREFIX + "/groups/%s/summary/rooms/%s" % (group_id, room_id,)
+
+        return self.client.delete_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_group_categories(self, destination, group_id, requester_user_id):
+        """Get all categories in a group
+        """
+        path = PREFIX + "/groups/%s/categories" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_group_category(self, destination, group_id, requester_user_id, category_id):
+        """Get category info in a group
+        """
+        path = PREFIX + "/groups/%s/categories/%s" % (group_id, category_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def update_group_category(self, destination, group_id, requester_user_id, category_id,
+                              content):
+        """Update a category in a group
+        """
+        path = PREFIX + "/groups/%s/categories/%s" % (group_id, category_id,)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def delete_group_category(self, destination, group_id, requester_user_id,
+                              category_id):
+        """Delete a category in a group
+        """
+        path = PREFIX + "/groups/%s/categories/%s" % (group_id, category_id,)
+
+        return self.client.delete_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_group_roles(self, destination, group_id, requester_user_id):
+        """Get all roles in a group
+        """
+        path = PREFIX + "/groups/%s/roles" % (group_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def get_group_role(self, destination, group_id, requester_user_id, role_id):
+        """Get a roles info
+        """
+        path = PREFIX + "/groups/%s/roles/%s" % (group_id, role_id,)
+
+        return self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def update_group_role(self, destination, group_id, requester_user_id, role_id,
+                          content):
+        """Update a role in a group
+        """
+        path = PREFIX + "/groups/%s/roles/%s" % (group_id, role_id,)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def delete_group_role(self, destination, group_id, requester_user_id, role_id):
+        """Delete a role in a group
+        """
+        path = PREFIX + "/groups/%s/roles/%s" % (group_id, role_id,)
+
+        return self.client.delete_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def update_group_summary_user(self, destination, group_id, requester_user_id,
+                                  user_id, role_id, content):
+        """Update a users entry in a group
+        """
+        if role_id:
+            path = PREFIX + "/groups/%s/summary/roles/%s/users/%s" % (
+                group_id, role_id, user_id,
+            )
+        else:
+            path = PREFIX + "/groups/%s/summary/users/%s" % (group_id, user_id,)
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            data=content,
+            ignore_backoff=True,
+        )
+
+    @log_function
+    def delete_group_summary_user(self, destination, group_id, requester_user_id,
+                                  user_id, role_id):
+        """Delete a users entry in a group
+        """
+        if role_id:
+            path = PREFIX + "/groups/%s/summary/roles/%s/users/%s" % (
+                group_id, role_id, user_id,
+            )
+        else:
+            path = PREFIX + "/groups/%s/summary/users/%s" % (group_id, user_id,)
+
+        return self.client.delete_json(
+            destination=destination,
+            path=path,
+            args={"requester_user_id": requester_user_id},
+            ignore_backoff=True,
+        )
+
+    def bulk_get_publicised_groups(self, destination, user_ids):
+        """Get the groups a list of users are publicising
+        """
+
+        path = PREFIX + "/get_groups_publicised"
+
+        content = {"user_ids": user_ids}
+
+        return self.client.post_json(
+            destination=destination,
+            path=path,
+            data=content,
+            ignore_backoff=True,
+        )
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index a78f01e442..f0778c65c5 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -25,7 +25,7 @@ from synapse.http.servlet import (
 from synapse.util.ratelimitutils import FederationRateLimiter
 from synapse.util.versionstring import get_version_string
 from synapse.util.logcontext import preserve_fn
-from synapse.types import ThirdPartyInstanceID
+from synapse.types import ThirdPartyInstanceID, get_domain_from_id
 
 import functools
 import logging
@@ -609,6 +609,493 @@ class FederationVersionServlet(BaseFederationServlet):
         }))
 
 
+class FederationGroupsProfileServlet(BaseFederationServlet):
+    """Get the basic profile of a group on behalf of a user
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/profile$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_group_profile(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsSummaryServlet(BaseFederationServlet):
+    PATH = "/groups/(?P<group_id>[^/]*)/summary$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_group_summary(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.update_group_profile(
+            group_id, requester_user_id, content
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsRoomsServlet(BaseFederationServlet):
+    """Get the rooms in a group on behalf of a user
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/rooms$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_rooms_in_group(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsAddRoomsServlet(BaseFederationServlet):
+    """Add/remove room from group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/room/(?<room_id>)$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, room_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.add_room_to_group(
+            group_id, requester_user_id, room_id, content
+        )
+
+        defer.returnValue((200, new_content))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, origin, content, query, group_id, room_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.remove_room_from_group(
+            group_id, requester_user_id, room_id,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsUsersServlet(BaseFederationServlet):
+    """Get the users in a group on behalf of a user
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/users$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_users_in_group(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsInvitedUsersServlet(BaseFederationServlet):
+    """Get the users that have been invited to a group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/invited_users$"
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.get_invited_users_in_group(
+            group_id, requester_user_id
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsInviteServlet(BaseFederationServlet):
+    """Ask a group server to invite someone to the group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/invite$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.invite_to_group(
+            group_id, user_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsAcceptInviteServlet(BaseFederationServlet):
+    """Accept an invitation from the group server
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/accept_invite$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        if get_domain_from_id(user_id) != origin:
+            raise SynapseError(403, "user_id doesn't match origin")
+
+        new_content = yield self.handler.accept_invite(
+            group_id, user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsRemoveUserServlet(BaseFederationServlet):
+    """Leave or kick a user from the group
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/remove$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        new_content = yield self.handler.remove_user_from_group(
+            group_id, user_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsLocalInviteServlet(BaseFederationServlet):
+    """A group server has invited a local user
+    """
+    PATH = "/groups/local/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/invite$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        if get_domain_from_id(group_id) != origin:
+            raise SynapseError(403, "group_id doesn't match origin")
+
+        new_content = yield self.handler.on_invite(
+            group_id, user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsRemoveLocalUserServlet(BaseFederationServlet):
+    """A group server has removed a local user
+    """
+    PATH = "/groups/local/(?P<group_id>[^/]*)/users/(?P<user_id>[^/]*)/remove$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        if get_domain_from_id(group_id) != origin:
+            raise SynapseError(403, "user_id doesn't match origin")
+
+        new_content = yield self.handler.user_removed_from_group(
+            group_id, user_id, content,
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsRenewAttestaionServlet(BaseFederationServlet):
+    """A group or user's server renews their attestation
+    """
+    PATH = "/groups/(?P<group_id>[^/]*)/renew_attestation/(?P<user_id>[^/]*)$"
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, user_id):
+        # We don't need to check auth here as we check the attestation signatures
+
+        new_content = yield self.handler.on_renew_attestation(
+            group_id, user_id, content
+        )
+
+        defer.returnValue((200, new_content))
+
+
+class FederationGroupsSummaryRoomsServlet(BaseFederationServlet):
+    """Add/remove a room from the group summary, with optional category.
+
+    Matches both:
+        - /groups/:group/summary/rooms/:room_id
+        - /groups/:group/summary/categories/:category/rooms/:room_id
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/summary"
+        "(/categories/(?P<category_id>[^/]+))?"
+        "/rooms/(?P<room_id>[^/]*)$"
+    )
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, category_id, room_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if category_id == "":
+            raise SynapseError(400, "category_id cannot be empty string")
+
+        resp = yield self.handler.update_group_summary_room(
+            group_id, requester_user_id,
+            room_id=room_id,
+            category_id=category_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, origin, content, query, group_id, category_id, room_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if category_id == "":
+            raise SynapseError(400, "category_id cannot be empty string")
+
+        resp = yield self.handler.delete_group_summary_room(
+            group_id, requester_user_id,
+            room_id=room_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsCategoriesServlet(BaseFederationServlet):
+    """Get all categories for a group
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/categories/$"
+    )
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        resp = yield self.handler.get_group_categories(
+            group_id, requester_user_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsCategoryServlet(BaseFederationServlet):
+    """Add/remove/get a category in a group
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/categories/(?P<category_id>[^/]+)$"
+    )
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id, category_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        resp = yield self.handler.get_group_category(
+            group_id, requester_user_id, category_id
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, category_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if category_id == "":
+            raise SynapseError(400, "category_id cannot be empty string")
+
+        resp = yield self.handler.upsert_group_category(
+            group_id, requester_user_id, category_id, content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, origin, content, query, group_id, category_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if category_id == "":
+            raise SynapseError(400, "category_id cannot be empty string")
+
+        resp = yield self.handler.delete_group_category(
+            group_id, requester_user_id, category_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsRolesServlet(BaseFederationServlet):
+    """Get roles in a group
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/roles/$"
+    )
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        resp = yield self.handler.get_group_roles(
+            group_id, requester_user_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsRoleServlet(BaseFederationServlet):
+    """Add/remove/get a role in a group
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/roles/(?P<role_id>[^/]+)$"
+    )
+
+    @defer.inlineCallbacks
+    def on_GET(self, origin, content, query, group_id, role_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        resp = yield self.handler.get_group_role(
+            group_id, requester_user_id, role_id
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, role_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if role_id == "":
+            raise SynapseError(400, "role_id cannot be empty string")
+
+        resp = yield self.handler.update_group_role(
+            group_id, requester_user_id, role_id, content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, origin, content, query, group_id, role_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if role_id == "":
+            raise SynapseError(400, "role_id cannot be empty string")
+
+        resp = yield self.handler.delete_group_role(
+            group_id, requester_user_id, role_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsSummaryUsersServlet(BaseFederationServlet):
+    """Add/remove a user from the group summary, with optional role.
+
+    Matches both:
+        - /groups/:group/summary/users/:user_id
+        - /groups/:group/summary/roles/:role/users/:user_id
+    """
+    PATH = (
+        "/groups/(?P<group_id>[^/]*)/summary"
+        "(/roles/(?P<role_id>[^/]+))?"
+        "/users/(?P<user_id>[^/]*)$"
+    )
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query, group_id, role_id, user_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if role_id == "":
+            raise SynapseError(400, "role_id cannot be empty string")
+
+        resp = yield self.handler.update_group_summary_user(
+            group_id, requester_user_id,
+            user_id=user_id,
+            role_id=role_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, origin, content, query, group_id, role_id, user_id):
+        requester_user_id = parse_string_from_args(query, "requester_user_id")
+        if get_domain_from_id(requester_user_id) != origin:
+            raise SynapseError(403, "requester_user_id doesn't match origin")
+
+        if role_id == "":
+            raise SynapseError(400, "role_id cannot be empty string")
+
+        resp = yield self.handler.delete_group_summary_user(
+            group_id, requester_user_id,
+            user_id=user_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class FederationGroupsBulkPublicisedServlet(BaseFederationServlet):
+    """Get roles in a group
+    """
+    PATH = (
+        "/get_groups_publicised$"
+    )
+
+    @defer.inlineCallbacks
+    def on_POST(self, origin, content, query):
+        resp = yield self.handler.bulk_get_publicised_groups(
+            content["user_ids"], proxy=False,
+        )
+
+        defer.returnValue((200, resp))
+
+
 FEDERATION_SERVLET_CLASSES = (
     FederationSendServlet,
     FederationPullServlet,
@@ -635,10 +1122,40 @@ FEDERATION_SERVLET_CLASSES = (
     FederationVersionServlet,
 )
 
+
 ROOM_LIST_CLASSES = (
     PublicRoomList,
 )
 
+GROUP_SERVER_SERVLET_CLASSES = (
+    FederationGroupsProfileServlet,
+    FederationGroupsSummaryServlet,
+    FederationGroupsRoomsServlet,
+    FederationGroupsUsersServlet,
+    FederationGroupsInvitedUsersServlet,
+    FederationGroupsInviteServlet,
+    FederationGroupsAcceptInviteServlet,
+    FederationGroupsRemoveUserServlet,
+    FederationGroupsSummaryRoomsServlet,
+    FederationGroupsCategoriesServlet,
+    FederationGroupsCategoryServlet,
+    FederationGroupsRolesServlet,
+    FederationGroupsRoleServlet,
+    FederationGroupsSummaryUsersServlet,
+)
+
+
+GROUP_LOCAL_SERVLET_CLASSES = (
+    FederationGroupsLocalInviteServlet,
+    FederationGroupsRemoveLocalUserServlet,
+    FederationGroupsBulkPublicisedServlet,
+)
+
+
+GROUP_ATTESTATION_SERVLET_CLASSES = (
+    FederationGroupsRenewAttestaionServlet,
+)
+
 
 def register_servlets(hs, resource, authenticator, ratelimiter):
     for servletclass in FEDERATION_SERVLET_CLASSES:
@@ -656,3 +1173,27 @@ def register_servlets(hs, resource, authenticator, ratelimiter):
             ratelimiter=ratelimiter,
             server_name=hs.hostname,
         ).register(resource)
+
+    for servletclass in GROUP_SERVER_SERVLET_CLASSES:
+        servletclass(
+            handler=hs.get_groups_server_handler(),
+            authenticator=authenticator,
+            ratelimiter=ratelimiter,
+            server_name=hs.hostname,
+        ).register(resource)
+
+    for servletclass in GROUP_LOCAL_SERVLET_CLASSES:
+        servletclass(
+            handler=hs.get_groups_local_handler(),
+            authenticator=authenticator,
+            ratelimiter=ratelimiter,
+            server_name=hs.hostname,
+        ).register(resource)
+
+    for servletclass in GROUP_ATTESTATION_SERVLET_CLASSES:
+        servletclass(
+            handler=hs.get_groups_attestation_renewer(),
+            authenticator=authenticator,
+            ratelimiter=ratelimiter,
+            server_name=hs.hostname,
+        ).register(resource)
diff --git a/synapse/groups/__init__.py b/synapse/groups/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/synapse/groups/__init__.py
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py
new file mode 100644
index 0000000000..b751cf5e43
--- /dev/null
+++ b/synapse/groups/attestations.py
@@ -0,0 +1,151 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.internet import defer
+
+from synapse.api.errors import SynapseError
+from synapse.types import get_domain_from_id
+from synapse.util.logcontext import preserve_fn
+
+from signedjson.sign import sign_json
+
+
+# Default validity duration for new attestations we create
+DEFAULT_ATTESTATION_LENGTH_MS = 3 * 24 * 60 * 60 * 1000
+
+# Start trying to update our attestations when they come this close to expiring
+UPDATE_ATTESTATION_TIME_MS = 1 * 24 * 60 * 60 * 1000
+
+
+class GroupAttestationSigning(object):
+    """Creates and verifies group attestations.
+    """
+    def __init__(self, hs):
+        self.keyring = hs.get_keyring()
+        self.clock = hs.get_clock()
+        self.server_name = hs.hostname
+        self.signing_key = hs.config.signing_key[0]
+
+    @defer.inlineCallbacks
+    def verify_attestation(self, attestation, group_id, user_id, server_name=None):
+        """Verifies that the given attestation matches the given parameters.
+
+        An optional server_name can be supplied to explicitly set which server's
+        signature is expected. Otherwise assumes that either the group_id or user_id
+        is local and uses the other's server as the one to check.
+        """
+
+        if not server_name:
+            if get_domain_from_id(group_id) == self.server_name:
+                server_name = get_domain_from_id(user_id)
+            elif get_domain_from_id(user_id) == self.server_name:
+                server_name = get_domain_from_id(group_id)
+            else:
+                raise Exception("Expected either group_id or user_id to be local")
+
+        if user_id != attestation["user_id"]:
+            raise SynapseError(400, "Attestation has incorrect user_id")
+
+        if group_id != attestation["group_id"]:
+            raise SynapseError(400, "Attestation has incorrect group_id")
+        valid_until_ms = attestation["valid_until_ms"]
+
+        # TODO: We also want to check that *new* attestations that people give
+        # us to store are valid for at least a little while.
+        if valid_until_ms < self.clock.time_msec():
+            raise SynapseError(400, "Attestation expired")
+
+        yield self.keyring.verify_json_for_server(server_name, attestation)
+
+    def create_attestation(self, group_id, user_id):
+        """Create an attestation for the group_id and user_id with default
+        validity length.
+        """
+        return sign_json({
+            "group_id": group_id,
+            "user_id": user_id,
+            "valid_until_ms": self.clock.time_msec() + DEFAULT_ATTESTATION_LENGTH_MS,
+        }, self.server_name, self.signing_key)
+
+
+class GroupAttestionRenewer(object):
+    """Responsible for sending and receiving attestation updates.
+    """
+
+    def __init__(self, hs):
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastore()
+        self.assestations = hs.get_groups_attestation_signing()
+        self.transport_client = hs.get_federation_transport_client()
+        self.is_mine_id = hs.is_mine_id
+        self.attestations = hs.get_groups_attestation_signing()
+
+        self._renew_attestations_loop = self.clock.looping_call(
+            self._renew_attestations, 30 * 60 * 1000,
+        )
+
+    @defer.inlineCallbacks
+    def on_renew_attestation(self, group_id, user_id, content):
+        """When a remote updates an attestation
+        """
+        attestation = content["attestation"]
+
+        if not self.is_mine_id(group_id) and not self.is_mine_id(user_id):
+            raise SynapseError(400, "Neither user not group are on this server")
+
+        yield self.attestations.verify_attestation(
+            attestation,
+            user_id=user_id,
+            group_id=group_id,
+        )
+
+        yield self.store.update_remote_attestion(group_id, user_id, attestation)
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def _renew_attestations(self):
+        """Called periodically to check if we need to update any of our attestations
+        """
+
+        now = self.clock.time_msec()
+
+        rows = yield self.store.get_attestations_need_renewals(
+            now + UPDATE_ATTESTATION_TIME_MS
+        )
+
+        @defer.inlineCallbacks
+        def _renew_attestation(group_id, user_id):
+            attestation = self.attestations.create_attestation(group_id, user_id)
+
+            if self.is_mine_id(group_id):
+                destination = get_domain_from_id(user_id)
+            else:
+                destination = get_domain_from_id(group_id)
+
+            yield self.transport_client.renew_group_attestation(
+                destination, group_id, user_id,
+                content={"attestation": attestation},
+            )
+
+            yield self.store.update_attestation_renewal(
+                group_id, user_id, attestation
+            )
+
+        for row in rows:
+            group_id = row["group_id"]
+            user_id = row["user_id"]
+
+            preserve_fn(_renew_attestation)(group_id, user_id)
diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
new file mode 100644
index 0000000000..fc4edb7f04
--- /dev/null
+++ b/synapse/groups/groups_server.py
@@ -0,0 +1,803 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.internet import defer
+
+from synapse.api.errors import SynapseError
+from synapse.types import UserID, get_domain_from_id, RoomID, GroupID
+
+
+import logging
+import urllib
+
+logger = logging.getLogger(__name__)
+
+
+# TODO: Allow users to "knock" or simpkly join depending on rules
+# TODO: Federation admin APIs
+# TODO: is_priveged flag to users and is_public to users and rooms
+# TODO: Audit log for admins (profile updates, membership changes, users who tried
+#       to join but were rejected, etc)
+# TODO: Flairs
+
+
+class GroupsServerHandler(object):
+    def __init__(self, hs):
+        self.hs = hs
+        self.store = hs.get_datastore()
+        self.room_list_handler = hs.get_room_list_handler()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.keyring = hs.get_keyring()
+        self.is_mine_id = hs.is_mine_id
+        self.signing_key = hs.config.signing_key[0]
+        self.server_name = hs.hostname
+        self.attestations = hs.get_groups_attestation_signing()
+        self.transport_client = hs.get_federation_transport_client()
+        self.profile_handler = hs.get_profile_handler()
+
+        # Ensure attestations get renewed
+        hs.get_groups_attestation_renewer()
+
+    @defer.inlineCallbacks
+    def check_group_is_ours(self, group_id, and_exists=False, and_is_admin=None):
+        """Check that the group is ours, and optionally if it exists.
+
+        If group does exist then return group.
+
+        Args:
+            group_id (str)
+            and_exists (bool): whether to also check if group exists
+            and_is_admin (str): whether to also check if given str is a user_id
+                that is an admin
+        """
+        if not self.is_mine_id(group_id):
+            raise SynapseError(400, "Group not on this server")
+
+        group = yield self.store.get_group(group_id)
+        if and_exists and not group:
+            raise SynapseError(404, "Unknown group")
+
+        if and_is_admin:
+            is_admin = yield self.store.is_user_admin_in_group(group_id, and_is_admin)
+            if not is_admin:
+                raise SynapseError(403, "User is not admin in group")
+
+        defer.returnValue(group)
+
+    @defer.inlineCallbacks
+    def get_group_summary(self, group_id, requester_user_id):
+        """Get the summary for a group as seen by requester_user_id.
+
+        The group summary consists of the profile of the room, and a curated
+        list of users and rooms. These list *may* be organised by role/category.
+        The roles/categories are ordered, and so are the users/rooms within them.
+
+        A user/room may appear in multiple roles/categories.
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
+
+        profile = yield self.get_group_profile(group_id, requester_user_id)
+
+        users, roles = yield self.store.get_users_for_summary_by_role(
+            group_id, include_private=is_user_in_group,
+        )
+
+        # TODO: Add profiles to users
+
+        rooms, categories = yield self.store.get_rooms_for_summary_by_category(
+            group_id, include_private=is_user_in_group,
+        )
+
+        for room_entry in rooms:
+            room_id = room_entry["room_id"]
+            joined_users = yield self.store.get_users_in_room(room_id)
+            entry = yield self.room_list_handler.generate_room_entry(
+                room_id, len(joined_users),
+                with_alias=False, allow_private=True,
+            )
+            entry = dict(entry)  # so we don't change whats cached
+            entry.pop("room_id", None)
+
+            room_entry["profile"] = entry
+
+        rooms.sort(key=lambda e: e.get("order", 0))
+
+        for entry in users:
+            user_id = entry["user_id"]
+
+            if not self.is_mine_id(requester_user_id):
+                attestation = yield self.store.get_remote_attestation(group_id, user_id)
+                if not attestation:
+                    continue
+
+                entry["attestation"] = attestation
+            else:
+                entry["attestation"] = self.attestations.create_attestation(
+                    group_id, user_id,
+                )
+
+            user_profile = yield self.profile_handler.get_profile_from_cache(user_id)
+            entry.update(user_profile)
+
+        users.sort(key=lambda e: e.get("order", 0))
+
+        membership_info = yield self.store.get_users_membership_info_in_group(
+            group_id, requester_user_id,
+        )
+
+        defer.returnValue({
+            "profile": profile,
+            "users_section": {
+                "users": users,
+                "roles": roles,
+                "total_user_count_estimate": 0,  # TODO
+            },
+            "rooms_section": {
+                "rooms": rooms,
+                "categories": categories,
+                "total_room_count_estimate": 0,  # TODO
+            },
+            "user": membership_info,
+        })
+
+    @defer.inlineCallbacks
+    def update_group_summary_room(self, group_id, user_id, room_id, category_id, content):
+        """Add/update a room to the group summary
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        RoomID.from_string(room_id)  # Ensure valid room id
+
+        order = content.get("order", None)
+
+        is_public = _parse_visibility_from_contents(content)
+
+        yield self.store.add_room_to_summary(
+            group_id=group_id,
+            room_id=room_id,
+            category_id=category_id,
+            order=order,
+            is_public=is_public,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def delete_group_summary_room(self, group_id, user_id, room_id, category_id):
+        """Remove a room from the summary
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        yield self.store.remove_room_from_summary(
+            group_id=group_id,
+            room_id=room_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def get_group_categories(self, group_id, user_id):
+        """Get all categories in a group (as seen by user)
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        categories = yield self.store.get_group_categories(
+            group_id=group_id,
+        )
+        defer.returnValue({"categories": categories})
+
+    @defer.inlineCallbacks
+    def get_group_category(self, group_id, user_id, category_id):
+        """Get a specific category in a group (as seen by user)
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        res = yield self.store.get_group_category(
+            group_id=group_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def update_group_category(self, group_id, user_id, category_id, content):
+        """Add/Update a group category
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        is_public = _parse_visibility_from_contents(content)
+        profile = content.get("profile")
+
+        yield self.store.upsert_group_category(
+            group_id=group_id,
+            category_id=category_id,
+            is_public=is_public,
+            profile=profile,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def delete_group_category(self, group_id, user_id, category_id):
+        """Delete a group category
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        yield self.store.remove_group_category(
+            group_id=group_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def get_group_roles(self, group_id, user_id):
+        """Get all roles in a group (as seen by user)
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        roles = yield self.store.get_group_roles(
+            group_id=group_id,
+        )
+        defer.returnValue({"roles": roles})
+
+    @defer.inlineCallbacks
+    def get_group_role(self, group_id, user_id, role_id):
+        """Get a specific role in a group (as seen by user)
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        res = yield self.store.get_group_role(
+            group_id=group_id,
+            role_id=role_id,
+        )
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def update_group_role(self, group_id, user_id, role_id, content):
+        """Add/update a role in a group
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        is_public = _parse_visibility_from_contents(content)
+
+        profile = content.get("profile")
+
+        yield self.store.upsert_group_role(
+            group_id=group_id,
+            role_id=role_id,
+            is_public=is_public,
+            profile=profile,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def delete_group_role(self, group_id, user_id, role_id):
+        """Remove role from group
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True, and_is_admin=user_id)
+
+        yield self.store.remove_group_role(
+            group_id=group_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def update_group_summary_user(self, group_id, requester_user_id, user_id, role_id,
+                                  content):
+        """Add/update a users entry in the group summary
+        """
+        yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id,
+        )
+
+        order = content.get("order", None)
+
+        is_public = _parse_visibility_from_contents(content)
+
+        yield self.store.add_user_to_summary(
+            group_id=group_id,
+            user_id=user_id,
+            role_id=role_id,
+            order=order,
+            is_public=is_public,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def delete_group_summary_user(self, group_id, requester_user_id, user_id, role_id):
+        """Remove a user from the group summary
+        """
+        yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id,
+        )
+
+        yield self.store.remove_user_from_summary(
+            group_id=group_id,
+            user_id=user_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def get_group_profile(self, group_id, requester_user_id):
+        """Get the group profile as seen by requester_user_id
+        """
+
+        yield self.check_group_is_ours(group_id)
+
+        group_description = yield self.store.get_group(group_id)
+
+        if group_description:
+            defer.returnValue(group_description)
+        else:
+            raise SynapseError(404, "Unknown group")
+
+    @defer.inlineCallbacks
+    def update_group_profile(self, group_id, requester_user_id, content):
+        """Update the group profile
+        """
+        yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id,
+        )
+
+        profile = {}
+        for keyname in ("name", "avatar_url", "short_description",
+                        "long_description"):
+            if keyname in content:
+                value = content[keyname]
+                if not isinstance(value, basestring):
+                    raise SynapseError(400, "%r value is not a string" % (keyname,))
+                profile[keyname] = value
+
+        yield self.store.update_group_profile(group_id, profile)
+
+    @defer.inlineCallbacks
+    def get_users_in_group(self, group_id, requester_user_id):
+        """Get the users in group as seen by requester_user_id.
+
+        The ordering is arbitrary at the moment
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
+
+        user_results = yield self.store.get_users_in_group(
+            group_id, include_private=is_user_in_group,
+        )
+
+        chunk = []
+        for user_result in user_results:
+            g_user_id = user_result["user_id"]
+            is_public = user_result["is_public"]
+
+            entry = {"user_id": g_user_id}
+
+            profile = yield self.profile_handler.get_profile_from_cache(g_user_id)
+            entry.update(profile)
+
+            if not is_public:
+                entry["is_public"] = False
+
+            if not self.is_mine_id(g_user_id):
+                attestation = yield self.store.get_remote_attestation(group_id, g_user_id)
+                if not attestation:
+                    continue
+
+                entry["attestation"] = attestation
+            else:
+                entry["attestation"] = self.attestations.create_attestation(
+                    group_id, g_user_id,
+                )
+
+            chunk.append(entry)
+
+        # TODO: If admin add lists of users whose attestations have timed out
+
+        defer.returnValue({
+            "chunk": chunk,
+            "total_user_count_estimate": len(user_results),
+        })
+
+    @defer.inlineCallbacks
+    def get_invited_users_in_group(self, group_id, requester_user_id):
+        """Get the users that have been invited to a group as seen by requester_user_id.
+
+        The ordering is arbitrary at the moment
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
+
+        if not is_user_in_group:
+            raise SynapseError(403, "User not in group")
+
+        invited_users = yield self.store.get_invited_users_in_group(group_id)
+
+        user_profiles = []
+
+        for user_id in invited_users:
+            user_profile = {
+                "user_id": user_id
+            }
+            try:
+                profile = yield self.profile_handler.get_profile_from_cache(user_id)
+                user_profile.update(profile)
+            except Exception as e:
+                logger.warn("Error getting profile for %s: %s", user_id, e)
+            user_profiles.append(user_profile)
+
+        defer.returnValue({
+            "chunk": user_profiles,
+            "total_user_count_estimate": len(invited_users),
+        })
+
+    @defer.inlineCallbacks
+    def get_rooms_in_group(self, group_id, requester_user_id):
+        """Get the rooms in group as seen by requester_user_id
+
+        This returns rooms in order of decreasing number of joined users
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
+
+        room_results = yield self.store.get_rooms_in_group(
+            group_id, include_private=is_user_in_group,
+        )
+
+        chunk = []
+        for room_result in room_results:
+            room_id = room_result["room_id"]
+            is_public = room_result["is_public"]
+
+            joined_users = yield self.store.get_users_in_room(room_id)
+            entry = yield self.room_list_handler.generate_room_entry(
+                room_id, len(joined_users),
+                with_alias=False, allow_private=True,
+            )
+
+            if not entry:
+                continue
+
+            if not is_public:
+                entry["is_public"] = False
+
+            chunk.append(entry)
+
+        chunk.sort(key=lambda e: -e["num_joined_members"])
+
+        defer.returnValue({
+            "chunk": chunk,
+            "total_room_count_estimate": len(room_results),
+        })
+
+    @defer.inlineCallbacks
+    def add_room_to_group(self, group_id, requester_user_id, room_id, content):
+        """Add room to group
+        """
+        RoomID.from_string(room_id)  # Ensure valid room id
+
+        yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id
+        )
+
+        is_public = _parse_visibility_from_contents(content)
+
+        yield self.store.add_room_to_group(group_id, room_id, is_public=is_public)
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def remove_room_from_group(self, group_id, requester_user_id, room_id):
+        """Remove room from group
+        """
+        yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id
+        )
+
+        yield self.store.remove_room_from_group(group_id, room_id)
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def invite_to_group(self, group_id, user_id, requester_user_id, content):
+        """Invite user to group
+        """
+
+        group = yield self.check_group_is_ours(
+            group_id, and_exists=True, and_is_admin=requester_user_id
+        )
+
+        # TODO: Check if user knocked
+        # TODO: Check if user is already invited
+
+        content = {
+            "profile": {
+                "name": group["name"],
+                "avatar_url": group["avatar_url"],
+            },
+            "inviter": requester_user_id,
+        }
+
+        if self.hs.is_mine_id(user_id):
+            groups_local = self.hs.get_groups_local_handler()
+            res = yield groups_local.on_invite(group_id, user_id, content)
+            local_attestation = None
+        else:
+            local_attestation = self.attestations.create_attestation(group_id, user_id)
+            content.update({
+                "attestation": local_attestation,
+            })
+
+            res = yield self.transport_client.invite_to_group_notification(
+                get_domain_from_id(user_id), group_id, user_id, content
+            )
+
+            user_profile = res.get("user_profile", {})
+            yield self.store.add_remote_profile_cache(
+                user_id,
+                displayname=user_profile.get("displayname"),
+                avatar_url=user_profile.get("avatar_url"),
+            )
+
+        if res["state"] == "join":
+            if not self.hs.is_mine_id(user_id):
+                remote_attestation = res["attestation"]
+
+                yield self.attestations.verify_attestation(
+                    remote_attestation,
+                    user_id=user_id,
+                    group_id=group_id,
+                )
+            else:
+                remote_attestation = None
+
+            yield self.store.add_user_to_group(
+                group_id, user_id,
+                is_admin=False,
+                is_public=False,  # TODO
+                local_attestation=local_attestation,
+                remote_attestation=remote_attestation,
+            )
+        elif res["state"] == "invite":
+            yield self.store.add_group_invite(
+                group_id, user_id,
+            )
+            defer.returnValue({
+                "state": "invite"
+            })
+        elif res["state"] == "reject":
+            defer.returnValue({
+                "state": "reject"
+            })
+        else:
+            raise SynapseError(502, "Unknown state returned by HS")
+
+    @defer.inlineCallbacks
+    def accept_invite(self, group_id, user_id, content):
+        """User tries to accept an invite to the group.
+
+        This is different from them asking to join, and so should error if no
+        invite exists (and they're not a member of the group)
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        if not self.store.is_user_invited_to_local_group(group_id, user_id):
+            raise SynapseError(403, "User not invited to group")
+
+        if not self.hs.is_mine_id(user_id):
+            remote_attestation = content["attestation"]
+
+            yield self.attestations.verify_attestation(
+                remote_attestation,
+                user_id=user_id,
+                group_id=group_id,
+            )
+        else:
+            remote_attestation = None
+
+        local_attestation = self.attestations.create_attestation(group_id, user_id)
+
+        is_public = _parse_visibility_from_contents(content)
+
+        yield self.store.add_user_to_group(
+            group_id, user_id,
+            is_admin=False,
+            is_public=is_public,
+            local_attestation=local_attestation,
+            remote_attestation=remote_attestation,
+        )
+
+        defer.returnValue({
+            "state": "join",
+            "attestation": local_attestation,
+        })
+
+    @defer.inlineCallbacks
+    def knock(self, group_id, user_id, content):
+        """A user requests becoming a member of the group
+        """
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        raise NotImplementedError()
+
+    @defer.inlineCallbacks
+    def accept_knock(self, group_id, user_id, content):
+        """Accept a users knock to the room.
+
+        Errors if the user hasn't knocked, rather than inviting them.
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        raise NotImplementedError()
+
+    @defer.inlineCallbacks
+    def remove_user_from_group(self, group_id, user_id, requester_user_id, content):
+        """Remove a user from the group; either a user is leaving or and admin
+        kicked htem.
+        """
+
+        yield self.check_group_is_ours(group_id, and_exists=True)
+
+        is_kick = False
+        if requester_user_id != user_id:
+            is_admin = yield self.store.is_user_admin_in_group(
+                group_id, requester_user_id
+            )
+            if not is_admin:
+                raise SynapseError(403, "User is not admin in group")
+
+            is_kick = True
+
+        yield self.store.remove_user_from_group(
+            group_id, user_id,
+        )
+
+        if is_kick:
+            if self.hs.is_mine_id(user_id):
+                groups_local = self.hs.get_groups_local_handler()
+                yield groups_local.user_removed_from_group(group_id, user_id, {})
+            else:
+                yield self.transport_client.remove_user_from_group_notification(
+                    get_domain_from_id(user_id), group_id, user_id, {}
+                )
+
+        if not self.hs.is_mine_id(user_id):
+            yield self.store.maybe_delete_remote_profile_cache(user_id)
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def create_group(self, group_id, user_id, content):
+        group = yield self.check_group_is_ours(group_id)
+
+        _validate_group_id(group_id)
+
+        logger.info("Attempting to create group with ID: %r", group_id)
+        if group:
+            raise SynapseError(400, "Group already exists")
+
+        is_admin = yield self.auth.is_server_admin(UserID.from_string(user_id))
+        if not is_admin:
+            if not self.hs.config.enable_group_creation:
+                raise SynapseError(
+                    403, "Only server admin can create group on this server",
+                )
+            localpart = GroupID.from_string(group_id).localpart
+            if not localpart.startswith(self.hs.config.group_creation_prefix):
+                raise SynapseError(
+                    400,
+                    "Can only create groups with prefix %r on this server" % (
+                        self.hs.config.group_creation_prefix,
+                    ),
+                )
+
+        profile = content.get("profile", {})
+        name = profile.get("name")
+        avatar_url = profile.get("avatar_url")
+        short_description = profile.get("short_description")
+        long_description = profile.get("long_description")
+        user_profile = content.get("user_profile", {})
+
+        yield self.store.create_group(
+            group_id,
+            user_id,
+            name=name,
+            avatar_url=avatar_url,
+            short_description=short_description,
+            long_description=long_description,
+        )
+
+        if not self.hs.is_mine_id(user_id):
+            remote_attestation = content["attestation"]
+
+            yield self.attestations.verify_attestation(
+                remote_attestation,
+                user_id=user_id,
+                group_id=group_id,
+            )
+
+            local_attestation = self.attestations.create_attestation(group_id, user_id)
+        else:
+            local_attestation = None
+            remote_attestation = None
+
+        yield self.store.add_user_to_group(
+            group_id, user_id,
+            is_admin=True,
+            is_public=True,  # TODO
+            local_attestation=local_attestation,
+            remote_attestation=remote_attestation,
+        )
+
+        if not self.hs.is_mine_id(user_id):
+            yield self.store.add_remote_profile_cache(
+                user_id,
+                displayname=user_profile.get("displayname"),
+                avatar_url=user_profile.get("avatar_url"),
+            )
+
+        defer.returnValue({
+            "group_id": group_id,
+        })
+
+
+def _parse_visibility_from_contents(content):
+    """Given a content for a request parse out whether the entity should be
+    public or not
+    """
+
+    visibility = content.get("visibility")
+    if visibility:
+        vis_type = visibility["type"]
+        if vis_type not in ("public", "private"):
+            raise SynapseError(
+                400, "Synapse only supports 'public'/'private' visibility"
+            )
+        is_public = vis_type == "public"
+    else:
+        is_public = True
+
+    return is_public
+
+
+def _validate_group_id(group_id):
+    """Validates the group ID is valid for creation on this home server
+    """
+    localpart = GroupID.from_string(group_id).localpart
+
+    if localpart.lower() != localpart:
+        raise SynapseError(400, "Group ID must be lower case")
+
+    if urllib.quote(localpart.encode('utf-8')) != localpart:
+        raise SynapseError(
+            400,
+            "Group ID can only contain characters a-z, 0-9, or '_-./'",
+        )
diff --git a/synapse/handlers/__init__.py b/synapse/handlers/__init__.py
index 5ad408f549..53213cdccf 100644
--- a/synapse/handlers/__init__.py
+++ b/synapse/handlers/__init__.py
@@ -20,7 +20,6 @@ from .room import (
 from .room_member import RoomMemberHandler
 from .message import MessageHandler
 from .federation import FederationHandler
-from .profile import ProfileHandler
 from .directory import DirectoryHandler
 from .admin import AdminHandler
 from .identity import IdentityHandler
@@ -52,7 +51,6 @@ class Handlers(object):
         self.room_creation_handler = RoomCreationHandler(hs)
         self.room_member_handler = RoomMemberHandler(hs)
         self.federation_handler = FederationHandler(hs)
-        self.profile_handler = ProfileHandler(hs)
         self.directory_handler = DirectoryHandler(hs)
         self.admin_handler = AdminHandler(hs)
         self.identity_handler = IdentityHandler(hs)
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index 943554ce98..a0464ae5c0 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -40,6 +40,8 @@ class DirectoryHandler(BaseHandler):
             "directory", self.on_directory_query
         )
 
+        self.spam_checker = hs.get_spam_checker()
+
     @defer.inlineCallbacks
     def _create_association(self, room_alias, room_id, servers=None, creator=None):
         # general association creation for both human users and app services
@@ -73,6 +75,11 @@ class DirectoryHandler(BaseHandler):
         # association creation for human users
         # TODO(erikj): Do user auth.
 
+        if not self.spam_checker.user_may_create_room_alias(user_id, room_alias):
+            raise SynapseError(
+                403, "This user is not permitted to create this alias",
+            )
+
         can_create = yield self.can_modify_alias(
             room_alias,
             user_id=user_id
@@ -327,6 +334,14 @@ class DirectoryHandler(BaseHandler):
         room_id (str)
         visibility (str): "public" or "private"
         """
+        if not self.spam_checker.user_may_publish_room(
+            requester.user.to_string(), room_id
+        ):
+            raise AuthError(
+                403,
+                "This user is not permitted to publish rooms to the room list"
+            )
+
         if requester.is_guest:
             raise AuthError(403, "Guests cannot edit the published room list")
 
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 18f87cad67..7711cded01 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -14,7 +14,6 @@
 # limitations under the License.
 
 """Contains handlers for federation events."""
-import synapse.util.logcontext
 from signedjson.key import decode_verify_key_bytes
 from signedjson.sign import verify_signed_json
 from unpaddedbase64 import decode_base64
@@ -26,10 +25,7 @@ from synapse.api.errors import (
 )
 from synapse.api.constants import EventTypes, Membership, RejectedReason
 from synapse.events.validator import EventValidator
-from synapse.util import unwrapFirstError
-from synapse.util.logcontext import (
-    preserve_fn, preserve_context_over_deferred
-)
+from synapse.util import unwrapFirstError, logcontext
 from synapse.util.metrics import measure_func
 from synapse.util.logutils import log_function
 from synapse.util.async import run_on_reactor, Linearizer
@@ -77,6 +73,7 @@ class FederationHandler(BaseHandler):
         self.action_generator = hs.get_action_generator()
         self.is_mine_id = hs.is_mine_id
         self.pusher_pool = hs.get_pusherpool()
+        self.spam_checker = hs.get_spam_checker()
 
         self.replication_layer.set_handler(self)
 
@@ -125,6 +122,28 @@ class FederationHandler(BaseHandler):
             self.room_queues[pdu.room_id].append((pdu, origin))
             return
 
+        # If we're no longer in the room just ditch the event entirely. This
+        # is probably an old server that has come back and thinks we're still
+        # in the room (or we've been rejoined to the room by a state reset).
+        #
+        # If we were never in the room then maybe our database got vaped and
+        # we should check if we *are* in fact in the room. If we are then we
+        # can magically rejoin the room.
+        is_in_room = yield self.auth.check_host_in_room(
+            pdu.room_id,
+            self.server_name
+        )
+        if not is_in_room:
+            was_in_room = yield self.store.was_host_joined(
+                pdu.room_id, self.server_name,
+            )
+            if was_in_room:
+                logger.info(
+                    "Ignoring PDU %s for room %s from %s as we've left the room!",
+                    pdu.event_id, pdu.room_id, origin,
+                )
+                return
+
         state = None
 
         auth_chain = []
@@ -591,9 +610,9 @@ class FederationHandler(BaseHandler):
                     missing_auth - failed_to_fetch
                 )
 
-                results = yield preserve_context_over_deferred(defer.gatherResults(
+                results = yield logcontext.make_deferred_yieldable(defer.gatherResults(
                     [
-                        preserve_fn(self.replication_layer.get_pdu)(
+                        logcontext.preserve_fn(self.replication_layer.get_pdu)(
                             [dest],
                             event_id,
                             outlier=True,
@@ -785,10 +804,14 @@ class FederationHandler(BaseHandler):
         event_ids = list(extremities.keys())
 
         logger.debug("calling resolve_state_groups in _maybe_backfill")
-        states = yield preserve_context_over_deferred(defer.gatherResults([
-            preserve_fn(self.state_handler.resolve_state_groups)(room_id, [e])
-            for e in event_ids
-        ]))
+        states = yield logcontext.make_deferred_yieldable(defer.gatherResults(
+            [
+                logcontext.preserve_fn(self.state_handler.resolve_state_groups)(
+                    room_id, [e]
+                )
+                for e in event_ids
+            ], consumeErrors=True,
+        ))
         states = dict(zip(event_ids, [s.state for s in states]))
 
         state_map = yield self.store.get_events(
@@ -941,9 +964,7 @@ class FederationHandler(BaseHandler):
             # lots of requests for missing prev_events which we do actually
             # have. Hence we fire off the deferred, but don't wait for it.
 
-            synapse.util.logcontext.preserve_fn(self._handle_queued_pdus)(
-                room_queue
-            )
+            logcontext.preserve_fn(self._handle_queued_pdus)(room_queue)
 
         defer.returnValue(True)
 
@@ -1070,6 +1091,9 @@ class FederationHandler(BaseHandler):
         """
         event = pdu
 
+        if event.state_key is None:
+            raise SynapseError(400, "The invite event did not have a state key")
+
         is_blocked = yield self.store.is_room_blocked(event.room_id)
         if is_blocked:
             raise SynapseError(403, "This room has been blocked on this server")
@@ -1077,6 +1101,13 @@ class FederationHandler(BaseHandler):
         if self.hs.config.block_non_admin_invites:
             raise SynapseError(403, "This server does not accept room invites")
 
+        if not self.spam_checker.user_may_invite(
+            event.sender, event.state_key, event.room_id,
+        ):
+            raise SynapseError(
+                403, "This user is not permitted to send invites to this server/user"
+            )
+
         membership = event.content.get("membership")
         if event.type != EventTypes.Member or membership != Membership.INVITE:
             raise SynapseError(400, "The event was not an m.room.member invite event")
@@ -1085,9 +1116,6 @@ class FederationHandler(BaseHandler):
         if sender_domain != origin:
             raise SynapseError(400, "The invite event was not from the server sending it")
 
-        if event.state_key is None:
-            raise SynapseError(400, "The invite event did not have a state key")
-
         if not self.is_mine_id(event.state_key):
             raise SynapseError(400, "The invite event must be for this server")
 
@@ -1430,7 +1458,7 @@ class FederationHandler(BaseHandler):
         if not backfilled:
             # this intentionally does not yield: we don't care about the result
             # and don't need to wait for it.
-            preserve_fn(self.pusher_pool.on_new_notifications)(
+            logcontext.preserve_fn(self.pusher_pool.on_new_notifications)(
                 event_stream_id, max_stream_id
             )
 
@@ -1443,16 +1471,16 @@ class FederationHandler(BaseHandler):
         a bunch of outliers, but not a chunk of individual events that depend
         on each other for state calculations.
         """
-        contexts = yield preserve_context_over_deferred(defer.gatherResults(
+        contexts = yield logcontext.make_deferred_yieldable(defer.gatherResults(
             [
-                preserve_fn(self._prep_event)(
+                logcontext.preserve_fn(self._prep_event)(
                     origin,
                     ev_info["event"],
                     state=ev_info.get("state"),
                     auth_events=ev_info.get("auth_events"),
                 )
                 for ev_info in event_infos
-            ]
+            ], consumeErrors=True,
         ))
 
         yield self.store.persist_events(
@@ -1760,18 +1788,17 @@ class FederationHandler(BaseHandler):
             # Do auth conflict res.
             logger.info("Different auth: %s", different_auth)
 
-            different_events = yield preserve_context_over_deferred(defer.gatherResults(
-                [
-                    preserve_fn(self.store.get_event)(
+            different_events = yield logcontext.make_deferred_yieldable(
+                defer.gatherResults([
+                    logcontext.preserve_fn(self.store.get_event)(
                         d,
                         allow_none=True,
                         allow_rejected=False,
                     )
                     for d in different_auth
                     if d in have_events and not have_events[d]
-                ],
-                consumeErrors=True
-            )).addErrback(unwrapFirstError)
+                ], consumeErrors=True)
+            ).addErrback(unwrapFirstError)
 
             if different_events:
                 local_view = dict(auth_events)
diff --git a/synapse/handlers/groups_local.py b/synapse/handlers/groups_local.py
new file mode 100644
index 0000000000..6699d0888f
--- /dev/null
+++ b/synapse/handlers/groups_local.py
@@ -0,0 +1,417 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.internet import defer
+
+from synapse.api.errors import SynapseError
+from synapse.types import get_domain_from_id
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def _create_rerouter(func_name):
+    """Returns a function that looks at the group id and calls the function
+    on federation or the local group server if the group is local
+    """
+    def f(self, group_id, *args, **kwargs):
+        if self.is_mine_id(group_id):
+            return getattr(self.groups_server_handler, func_name)(
+                group_id, *args, **kwargs
+            )
+        else:
+            destination = get_domain_from_id(group_id)
+            return getattr(self.transport_client, func_name)(
+                destination, group_id, *args, **kwargs
+            )
+    return f
+
+
+class GroupsLocalHandler(object):
+    def __init__(self, hs):
+        self.hs = hs
+        self.store = hs.get_datastore()
+        self.room_list_handler = hs.get_room_list_handler()
+        self.groups_server_handler = hs.get_groups_server_handler()
+        self.transport_client = hs.get_federation_transport_client()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.keyring = hs.get_keyring()
+        self.is_mine_id = hs.is_mine_id
+        self.signing_key = hs.config.signing_key[0]
+        self.server_name = hs.hostname
+        self.notifier = hs.get_notifier()
+        self.attestations = hs.get_groups_attestation_signing()
+
+        self.profile_handler = hs.get_profile_handler()
+
+        # Ensure attestations get renewed
+        hs.get_groups_attestation_renewer()
+
+    # The following functions merely route the query to the local groups server
+    # or federation depending on if the group is local or remote
+
+    get_group_profile = _create_rerouter("get_group_profile")
+    update_group_profile = _create_rerouter("update_group_profile")
+    get_rooms_in_group = _create_rerouter("get_rooms_in_group")
+
+    get_invited_users_in_group = _create_rerouter("get_invited_users_in_group")
+
+    add_room_to_group = _create_rerouter("add_room_to_group")
+    remove_room_from_group = _create_rerouter("remove_room_from_group")
+
+    update_group_summary_room = _create_rerouter("update_group_summary_room")
+    delete_group_summary_room = _create_rerouter("delete_group_summary_room")
+
+    update_group_category = _create_rerouter("update_group_category")
+    delete_group_category = _create_rerouter("delete_group_category")
+    get_group_category = _create_rerouter("get_group_category")
+    get_group_categories = _create_rerouter("get_group_categories")
+
+    update_group_summary_user = _create_rerouter("update_group_summary_user")
+    delete_group_summary_user = _create_rerouter("delete_group_summary_user")
+
+    update_group_role = _create_rerouter("update_group_role")
+    delete_group_role = _create_rerouter("delete_group_role")
+    get_group_role = _create_rerouter("get_group_role")
+    get_group_roles = _create_rerouter("get_group_roles")
+
+    @defer.inlineCallbacks
+    def get_group_summary(self, group_id, requester_user_id):
+        """Get the group summary for a group.
+
+        If the group is remote we check that the users have valid attestations.
+        """
+        if self.is_mine_id(group_id):
+            res = yield self.groups_server_handler.get_group_summary(
+                group_id, requester_user_id
+            )
+        else:
+            res = yield self.transport_client.get_group_summary(
+                get_domain_from_id(group_id), group_id, requester_user_id,
+            )
+
+            group_server_name = get_domain_from_id(group_id)
+
+            # Loop through the users and validate the attestations.
+            chunk = res["users_section"]["users"]
+            valid_users = []
+            for entry in chunk:
+                g_user_id = entry["user_id"]
+                attestation = entry.pop("attestation", {})
+                try:
+                    if get_domain_from_id(g_user_id) != group_server_name:
+                        yield self.attestations.verify_attestation(
+                            attestation,
+                            group_id=group_id,
+                            user_id=g_user_id,
+                            server_name=get_domain_from_id(g_user_id),
+                        )
+                    valid_users.append(entry)
+                except Exception as e:
+                    logger.info("Failed to verify user is in group: %s", e)
+
+            res["users_section"]["users"] = valid_users
+
+            res["users_section"]["users"].sort(key=lambda e: e.get("order", 0))
+            res["rooms_section"]["rooms"].sort(key=lambda e: e.get("order", 0))
+
+        # Add `is_publicised` flag to indicate whether the user has publicised their
+        # membership of the group on their profile
+        result = yield self.store.get_publicised_groups_for_user(requester_user_id)
+        is_publicised = group_id in result
+
+        res.setdefault("user", {})["is_publicised"] = is_publicised
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def create_group(self, group_id, user_id, content):
+        """Create a group
+        """
+
+        logger.info("Asking to create group with ID: %r", group_id)
+
+        if self.is_mine_id(group_id):
+            res = yield self.groups_server_handler.create_group(
+                group_id, user_id, content
+            )
+            local_attestation = None
+            remote_attestation = None
+        else:
+            local_attestation = self.attestations.create_attestation(group_id, user_id)
+            content["attestation"] = local_attestation
+
+            content["user_profile"] = yield self.profile_handler.get_profile(user_id)
+
+            res = yield self.transport_client.create_group(
+                get_domain_from_id(group_id), group_id, user_id, content,
+            )
+
+            remote_attestation = res["attestation"]
+            yield self.attestations.verify_attestation(
+                remote_attestation,
+                group_id=group_id,
+                user_id=user_id,
+                server_name=get_domain_from_id(group_id),
+            )
+
+        is_publicised = content.get("publicise", False)
+        token = yield self.store.register_user_group_membership(
+            group_id, user_id,
+            membership="join",
+            is_admin=True,
+            local_attestation=local_attestation,
+            remote_attestation=remote_attestation,
+            is_publicised=is_publicised,
+        )
+        self.notifier.on_new_event(
+            "groups_key", token, users=[user_id],
+        )
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def get_users_in_group(self, group_id, requester_user_id):
+        """Get users in a group
+        """
+        if self.is_mine_id(group_id):
+            res = yield self.groups_server_handler.get_users_in_group(
+                group_id, requester_user_id
+            )
+            defer.returnValue(res)
+
+        group_server_name = get_domain_from_id(group_id)
+
+        res = yield self.transport_client.get_users_in_group(
+            get_domain_from_id(group_id), group_id, requester_user_id,
+        )
+
+        chunk = res["chunk"]
+        valid_entries = []
+        for entry in chunk:
+            g_user_id = entry["user_id"]
+            attestation = entry.pop("attestation", {})
+            try:
+                if get_domain_from_id(g_user_id) != group_server_name:
+                    yield self.attestations.verify_attestation(
+                        attestation,
+                        group_id=group_id,
+                        user_id=g_user_id,
+                        server_name=get_domain_from_id(g_user_id),
+                    )
+                valid_entries.append(entry)
+            except Exception as e:
+                logger.info("Failed to verify user is in group: %s", e)
+
+        res["chunk"] = valid_entries
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def join_group(self, group_id, user_id, content):
+        """Request to join a group
+        """
+        raise NotImplementedError()  # TODO
+
+    @defer.inlineCallbacks
+    def accept_invite(self, group_id, user_id, content):
+        """Accept an invite to a group
+        """
+        if self.is_mine_id(group_id):
+            yield self.groups_server_handler.accept_invite(
+                group_id, user_id, content
+            )
+            local_attestation = None
+            remote_attestation = None
+        else:
+            local_attestation = self.attestations.create_attestation(group_id, user_id)
+            content["attestation"] = local_attestation
+
+            res = yield self.transport_client.accept_group_invite(
+                get_domain_from_id(group_id), group_id, user_id, content,
+            )
+
+            remote_attestation = res["attestation"]
+
+            yield self.attestations.verify_attestation(
+                remote_attestation,
+                group_id=group_id,
+                user_id=user_id,
+                server_name=get_domain_from_id(group_id),
+            )
+
+        # TODO: Check that the group is public and we're being added publically
+        is_publicised = content.get("publicise", False)
+
+        token = yield self.store.register_user_group_membership(
+            group_id, user_id,
+            membership="join",
+            is_admin=False,
+            local_attestation=local_attestation,
+            remote_attestation=remote_attestation,
+            is_publicised=is_publicised,
+        )
+        self.notifier.on_new_event(
+            "groups_key", token, users=[user_id],
+        )
+
+        defer.returnValue({})
+
+    @defer.inlineCallbacks
+    def invite(self, group_id, user_id, requester_user_id, config):
+        """Invite a user to a group
+        """
+        content = {
+            "requester_user_id": requester_user_id,
+            "config": config,
+        }
+        if self.is_mine_id(group_id):
+            res = yield self.groups_server_handler.invite_to_group(
+                group_id, user_id, requester_user_id, content,
+            )
+        else:
+            res = yield self.transport_client.invite_to_group(
+                get_domain_from_id(group_id), group_id, user_id, requester_user_id,
+                content,
+            )
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def on_invite(self, group_id, user_id, content):
+        """One of our users were invited to a group
+        """
+        # TODO: Support auto join and rejection
+
+        if not self.is_mine_id(user_id):
+            raise SynapseError(400, "User not on this server")
+
+        local_profile = {}
+        if "profile" in content:
+            if "name" in content["profile"]:
+                local_profile["name"] = content["profile"]["name"]
+            if "avatar_url" in content["profile"]:
+                local_profile["avatar_url"] = content["profile"]["avatar_url"]
+
+        token = yield self.store.register_user_group_membership(
+            group_id, user_id,
+            membership="invite",
+            content={"profile": local_profile, "inviter": content["inviter"]},
+        )
+        self.notifier.on_new_event(
+            "groups_key", token, users=[user_id],
+        )
+        try:
+            user_profile = yield self.profile_handler.get_profile(user_id)
+        except Exception as e:
+            logger.warn("No profile for user %s: %s", user_id, e)
+            user_profile = {}
+
+        defer.returnValue({"state": "invite", "user_profile": user_profile})
+
+    @defer.inlineCallbacks
+    def remove_user_from_group(self, group_id, user_id, requester_user_id, content):
+        """Remove a user from a group
+        """
+        if user_id == requester_user_id:
+            token = yield self.store.register_user_group_membership(
+                group_id, user_id,
+                membership="leave",
+            )
+            self.notifier.on_new_event(
+                "groups_key", token, users=[user_id],
+            )
+
+            # TODO: Should probably remember that we tried to leave so that we can
+            # retry if the group server is currently down.
+
+        if self.is_mine_id(group_id):
+            res = yield self.groups_server_handler.remove_user_from_group(
+                group_id, user_id, requester_user_id, content,
+            )
+        else:
+            content["requester_user_id"] = requester_user_id
+            res = yield self.transport_client.remove_user_from_group(
+                get_domain_from_id(group_id), group_id, requester_user_id,
+                user_id, content,
+            )
+
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def user_removed_from_group(self, group_id, user_id, content):
+        """One of our users was removed/kicked from a group
+        """
+        # TODO: Check if user in group
+        token = yield self.store.register_user_group_membership(
+            group_id, user_id,
+            membership="leave",
+        )
+        self.notifier.on_new_event(
+            "groups_key", token, users=[user_id],
+        )
+
+    @defer.inlineCallbacks
+    def get_joined_groups(self, user_id):
+        group_ids = yield self.store.get_joined_groups(user_id)
+        defer.returnValue({"groups": group_ids})
+
+    @defer.inlineCallbacks
+    def get_publicised_groups_for_user(self, user_id):
+        if self.hs.is_mine_id(user_id):
+            result = yield self.store.get_publicised_groups_for_user(user_id)
+            defer.returnValue({"groups": result})
+        else:
+            result = yield self.transport_client.get_publicised_groups_for_user(
+                get_domain_from_id(user_id), user_id
+            )
+            # TODO: Verify attestations
+            defer.returnValue(result)
+
+    @defer.inlineCallbacks
+    def bulk_get_publicised_groups(self, user_ids, proxy=True):
+        destinations = {}
+        local_users = set()
+
+        for user_id in user_ids:
+            if self.hs.is_mine_id(user_id):
+                local_users.add(user_id)
+            else:
+                destinations.setdefault(
+                    get_domain_from_id(user_id), set()
+                ).add(user_id)
+
+        if not proxy and destinations:
+            raise SynapseError(400, "Some user_ids are not local")
+
+        results = {}
+        failed_results = []
+        for destination, dest_user_ids in destinations.iteritems():
+            try:
+                r = yield self.transport_client.bulk_get_publicised_groups(
+                    destination, list(dest_user_ids),
+                )
+                results.update(r["users"])
+            except Exception:
+                failed_results.extend(dest_user_ids)
+
+        for uid in local_users:
+            results[uid] = yield self.store.get_publicised_groups_for_user(
+                uid
+            )
+
+        defer.returnValue({"users": results})
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index da18bf23db..28792788d9 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014 - 2016 OpenMarket Ltd
+# Copyright 2017 New Vector Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,7 +13,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from synapse.events import spamcheck
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
@@ -26,6 +26,7 @@ from synapse.types import (
 from synapse.util.async import run_on_reactor, ReadWriteLock, Limiter
 from synapse.util.logcontext import preserve_fn
 from synapse.util.metrics import measure_func
+from synapse.util.frozenutils import unfreeze
 from synapse.visibility import filter_events_for_client
 
 from ._base import BaseHandler
@@ -47,6 +48,7 @@ class MessageHandler(BaseHandler):
         self.state = hs.get_state_handler()
         self.clock = hs.get_clock()
         self.validator = EventValidator()
+        self.profile_handler = hs.get_profile_handler()
 
         self.pagination_lock = ReadWriteLock()
 
@@ -58,6 +60,8 @@ class MessageHandler(BaseHandler):
 
         self.action_generator = hs.get_action_generator()
 
+        self.spam_checker = hs.get_spam_checker()
+
     @defer.inlineCallbacks
     def purge_history(self, room_id, event_id):
         event = yield self.store.get_event(event_id)
@@ -210,7 +214,7 @@ class MessageHandler(BaseHandler):
 
                 if membership in {Membership.JOIN, Membership.INVITE}:
                     # If event doesn't include a display name, add one.
-                    profile = self.hs.get_handlers().profile_handler
+                    profile = self.profile_handler
                     content = builder.content
 
                     try:
@@ -322,9 +326,12 @@ class MessageHandler(BaseHandler):
             txn_id=txn_id
         )
 
-        if spamcheck.check_event_for_spam(event):
+        spam_error = self.spam_checker.check_event_for_spam(event)
+        if spam_error:
+            if not isinstance(spam_error, basestring):
+                spam_error = "Spam is not permitted here"
             raise SynapseError(
-                403, "Spam is not permitted here", Codes.FORBIDDEN
+                403, spam_error, Codes.FORBIDDEN
             )
 
         yield self.send_nonmember_event(
@@ -418,6 +425,51 @@ class MessageHandler(BaseHandler):
             [serialize_event(c, now) for c in room_state.values()]
         )
 
+    @defer.inlineCallbacks
+    def get_joined_members(self, requester, room_id):
+        """Get all the joined members in the room and their profile information.
+
+        If the user has left the room return the state events from when they left.
+
+        Args:
+            requester(Requester): The user requesting state events.
+            room_id(str): The room ID to get all state events from.
+        Returns:
+            A dict of user_id to profile info
+        """
+        user_id = requester.user.to_string()
+        if not requester.app_service:
+            # We check AS auth after fetching the room membership, as it
+            # requires us to pull out all joined members anyway.
+            membership, _ = yield self._check_in_room_or_world_readable(
+                room_id, user_id
+            )
+            if membership != Membership.JOIN:
+                raise NotImplementedError(
+                    "Getting joined members after leaving is not implemented"
+                )
+
+        users_with_profile = yield self.state.get_current_user_in_room(room_id)
+
+        # If this is an AS, double check that they are allowed to see the members.
+        # This can either be because the AS user is in the room or becuase there
+        # is a user in the room that the AS is "interested in"
+        if requester.app_service and user_id not in users_with_profile:
+            for uid in users_with_profile:
+                if requester.app_service.is_interested_in_user(uid):
+                    break
+            else:
+                # Loop fell through, AS has no interested users in room
+                raise AuthError(403, "Appservice not in room")
+
+        defer.returnValue({
+            user_id: {
+                "avatar_url": profile.avatar_url,
+                "display_name": profile.display_name,
+            }
+            for user_id, profile in users_with_profile.iteritems()
+        })
+
     @measure_func("_create_new_client_event")
     @defer.inlineCallbacks
     def _create_new_client_event(self, builder, requester=None, prev_event_ids=None):
@@ -509,7 +561,7 @@ class MessageHandler(BaseHandler):
 
         # Ensure that we can round trip before trying to persist in db
         try:
-            dump = ujson.dumps(event.content)
+            dump = ujson.dumps(unfreeze(event.content))
             ujson.loads(dump)
         except:
             logger.exception("Failed to encode content: %r", event.content)
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index 7abee98dea..e56e0a52bf 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -19,14 +19,15 @@ from twisted.internet import defer
 
 import synapse.types
 from synapse.api.errors import SynapseError, AuthError, CodeMessageException
-from synapse.types import UserID
+from synapse.types import UserID, get_domain_from_id
 from ._base import BaseHandler
 
-
 logger = logging.getLogger(__name__)
 
 
 class ProfileHandler(BaseHandler):
+    PROFILE_UPDATE_MS = 60 * 1000
+    PROFILE_UPDATE_EVERY_MS = 24 * 60 * 60 * 1000
 
     def __init__(self, hs):
         super(ProfileHandler, self).__init__(hs)
@@ -36,6 +37,63 @@ class ProfileHandler(BaseHandler):
             "profile", self.on_profile_query
         )
 
+        self.clock.looping_call(self._update_remote_profile_cache, self.PROFILE_UPDATE_MS)
+
+    @defer.inlineCallbacks
+    def get_profile(self, user_id):
+        target_user = UserID.from_string(user_id)
+        if self.hs.is_mine(target_user):
+            displayname = yield self.store.get_profile_displayname(
+                target_user.localpart
+            )
+            avatar_url = yield self.store.get_profile_avatar_url(
+                target_user.localpart
+            )
+
+            defer.returnValue({
+                "displayname": displayname,
+                "avatar_url": avatar_url,
+            })
+        else:
+            try:
+                result = yield self.federation.make_query(
+                    destination=target_user.domain,
+                    query_type="profile",
+                    args={
+                        "user_id": user_id,
+                    },
+                    ignore_backoff=True,
+                )
+                defer.returnValue(result)
+            except CodeMessageException as e:
+                if e.code != 404:
+                    logger.exception("Failed to get displayname")
+
+                raise
+
+    @defer.inlineCallbacks
+    def get_profile_from_cache(self, user_id):
+        """Get the profile information from our local cache. If the user is
+        ours then the profile information will always be corect. Otherwise,
+        it may be out of date/missing.
+        """
+        target_user = UserID.from_string(user_id)
+        if self.hs.is_mine(target_user):
+            displayname = yield self.store.get_profile_displayname(
+                target_user.localpart
+            )
+            avatar_url = yield self.store.get_profile_avatar_url(
+                target_user.localpart
+            )
+
+            defer.returnValue({
+                "displayname": displayname,
+                "avatar_url": avatar_url,
+            })
+        else:
+            profile = yield self.store.get_from_remote_profile_cache(user_id)
+            defer.returnValue(profile or {})
+
     @defer.inlineCallbacks
     def get_displayname(self, target_user):
         if self.hs.is_mine(target_user):
@@ -182,3 +240,44 @@ class ProfileHandler(BaseHandler):
                     "Failed to update join event for room %s - %s",
                     room_id, str(e.message)
                 )
+
+    def _update_remote_profile_cache(self):
+        """Called periodically to check profiles of remote users we haven't
+        checked in a while.
+        """
+        entries = yield self.store.get_remote_profile_cache_entries_that_expire(
+            last_checked=self.clock.time_msec() - self.PROFILE_UPDATE_EVERY_MS
+        )
+
+        for user_id, displayname, avatar_url in entries:
+            is_subscribed = yield self.store.is_subscribed_remote_profile_for_user(
+                user_id,
+            )
+            if not is_subscribed:
+                yield self.store.maybe_delete_remote_profile_cache(user_id)
+                continue
+
+            try:
+                profile = yield self.federation.make_query(
+                    destination=get_domain_from_id(user_id),
+                    query_type="profile",
+                    args={
+                        "user_id": user_id,
+                    },
+                    ignore_backoff=True,
+                )
+            except:
+                logger.exception("Failed to get avatar_url")
+
+                yield self.store.update_remote_profile_cache(
+                    user_id, displayname, avatar_url
+                )
+                continue
+
+            new_name = profile.get("displayname")
+            new_avatar = profile.get("avatar_url")
+
+            # We always hit update to update the last_check timestamp
+            yield self.store.update_remote_profile_cache(
+                user_id, new_name, new_avatar
+            )
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index e1cd3a48e9..0525765272 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from synapse.util import logcontext
 
 from ._base import BaseHandler
 
@@ -59,6 +60,8 @@ class ReceiptsHandler(BaseHandler):
         is_new = yield self._handle_new_receipts([receipt])
 
         if is_new:
+            # fire off a process in the background to send the receipt to
+            # remote servers
             self._push_remotes([receipt])
 
     @defer.inlineCallbacks
@@ -126,6 +129,7 @@ class ReceiptsHandler(BaseHandler):
 
             defer.returnValue(True)
 
+    @logcontext.preserve_fn   # caller should not yield on this
     @defer.inlineCallbacks
     def _push_remotes(self, receipts):
         """Given a list of receipts, works out which remote servers should be
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index ee3a2269a8..560fb36254 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -36,6 +36,7 @@ class RegistrationHandler(BaseHandler):
         super(RegistrationHandler, self).__init__(hs)
 
         self.auth = hs.get_auth()
+        self.profile_handler = hs.get_profile_handler()
         self.captcha_client = CaptchaServerHttpClient(hs)
 
         self._next_generated_user_id = None
@@ -423,8 +424,7 @@ class RegistrationHandler(BaseHandler):
 
         if displayname is not None:
             logger.info("setting user display name: %s -> %s", user_id, displayname)
-            profile_handler = self.hs.get_handlers().profile_handler
-            yield profile_handler.set_displayname(
+            yield self.profile_handler.set_displayname(
                 user, requester, displayname, by_admin=True,
             )
 
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 5698d28088..535ba9517c 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -60,6 +60,11 @@ class RoomCreationHandler(BaseHandler):
         },
     }
 
+    def __init__(self, hs):
+        super(RoomCreationHandler, self).__init__(hs)
+
+        self.spam_checker = hs.get_spam_checker()
+
     @defer.inlineCallbacks
     def create_room(self, requester, config, ratelimit=True):
         """ Creates a new room.
@@ -75,6 +80,9 @@ class RoomCreationHandler(BaseHandler):
         """
         user_id = requester.user.to_string()
 
+        if not self.spam_checker.user_may_create_room(user_id):
+            raise SynapseError(403, "You are not permitted to create rooms")
+
         if ratelimit:
             yield self.ratelimit(requester)
 
diff --git a/synapse/handlers/room_list.py b/synapse/handlers/room_list.py
index 516cd9a6ac..41e1781df7 100644
--- a/synapse/handlers/room_list.py
+++ b/synapse/handlers/room_list.py
@@ -276,13 +276,14 @@ class RoomListHandler(BaseHandler):
             # We've already got enough, so lets just drop it.
             return
 
-        result = yield self._generate_room_entry(room_id, num_joined_users)
+        result = yield self.generate_room_entry(room_id, num_joined_users)
 
         if result and _matches_room_entry(result, search_filter):
             chunk.append(result)
 
     @cachedInlineCallbacks(num_args=1, cache_context=True)
-    def _generate_room_entry(self, room_id, num_joined_users, cache_context):
+    def generate_room_entry(self, room_id, num_joined_users, cache_context,
+                            with_alias=True, allow_private=False):
         """Returns the entry for a room
         """
         result = {
@@ -316,14 +317,15 @@ class RoomListHandler(BaseHandler):
         join_rules_event = current_state.get((EventTypes.JoinRules, ""))
         if join_rules_event:
             join_rule = join_rules_event.content.get("join_rule", None)
-            if join_rule and join_rule != JoinRules.PUBLIC:
+            if not allow_private and join_rule and join_rule != JoinRules.PUBLIC:
                 defer.returnValue(None)
 
-        aliases = yield self.store.get_aliases_for_room(
-            room_id, on_invalidate=cache_context.invalidate
-        )
-        if aliases:
-            result["aliases"] = aliases
+        if with_alias:
+            aliases = yield self.store.get_aliases_for_room(
+                room_id, on_invalidate=cache_context.invalidate
+            )
+            if aliases:
+                result["aliases"] = aliases
 
         name_event = yield current_state.get((EventTypes.Name, ""))
         if name_event:
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 9a498c2d3e..970fec0666 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -45,9 +45,12 @@ class RoomMemberHandler(BaseHandler):
     def __init__(self, hs):
         super(RoomMemberHandler, self).__init__(hs)
 
+        self.profile_handler = hs.get_profile_handler()
+
         self.member_linearizer = Linearizer(name="member")
 
         self.clock = hs.get_clock()
+        self.spam_checker = hs.get_spam_checker()
 
         self.distributor = hs.get_distributor()
         self.distributor.declare("user_joined_room")
@@ -210,12 +213,26 @@ class RoomMemberHandler(BaseHandler):
             if is_blocked:
                 raise SynapseError(403, "This room has been blocked on this server")
 
-        if (effective_membership_state == "invite" and
-                self.hs.config.block_non_admin_invites):
+        if effective_membership_state == "invite":
+            block_invite = False
             is_requester_admin = yield self.auth.is_server_admin(
                 requester.user,
             )
             if not is_requester_admin:
+                if self.hs.config.block_non_admin_invites:
+                    logger.info(
+                        "Blocking invite: user is not admin and non-admin "
+                        "invites disabled"
+                    )
+                    block_invite = True
+
+                if not self.spam_checker.user_may_invite(
+                    requester.user.to_string(), target.to_string(), room_id,
+                ):
+                    logger.info("Blocking invite due to spam checker")
+                    block_invite = True
+
+            if block_invite:
                 raise SynapseError(
                     403, "Invites have been disabled on this server",
                 )
@@ -267,7 +284,7 @@ class RoomMemberHandler(BaseHandler):
 
                 content["membership"] = Membership.JOIN
 
-                profile = self.hs.get_handlers().profile_handler
+                profile = self.profile_handler
                 if not content_specified:
                     content["displayname"] = yield profile.get_displayname(target)
                     content["avatar_url"] = yield profile.get_avatar_url(target)
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index dd0ec00ae6..219529936f 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -108,6 +108,17 @@ class InvitedSyncResult(collections.namedtuple("InvitedSyncResult", [
         return True
 
 
+class GroupsSyncResult(collections.namedtuple("GroupsSyncResult", [
+    "join",
+    "invite",
+    "leave",
+])):
+    __slots__ = []
+
+    def __nonzero__(self):
+        return bool(self.join or self.invite or self.leave)
+
+
 class DeviceLists(collections.namedtuple("DeviceLists", [
     "changed",   # list of user_ids whose devices may have changed
     "left",      # list of user_ids whose devices we no longer track
@@ -129,6 +140,7 @@ class SyncResult(collections.namedtuple("SyncResult", [
     "device_lists",  # List of user_ids whose devices have chanegd
     "device_one_time_keys_count",  # Dict of algorithm to count for one time keys
                                    # for this device
+    "groups",
 ])):
     __slots__ = []
 
@@ -144,7 +156,8 @@ class SyncResult(collections.namedtuple("SyncResult", [
             self.archived or
             self.account_data or
             self.to_device or
-            self.device_lists
+            self.device_lists or
+            self.groups
         )
 
 
@@ -595,6 +608,8 @@ class SyncHandler(object):
                 user_id, device_id
             )
 
+        yield self._generate_sync_entry_for_groups(sync_result_builder)
+
         defer.returnValue(SyncResult(
             presence=sync_result_builder.presence,
             account_data=sync_result_builder.account_data,
@@ -603,10 +618,57 @@ class SyncHandler(object):
             archived=sync_result_builder.archived,
             to_device=sync_result_builder.to_device,
             device_lists=device_lists,
+            groups=sync_result_builder.groups,
             device_one_time_keys_count=one_time_key_counts,
             next_batch=sync_result_builder.now_token,
         ))
 
+    @measure_func("_generate_sync_entry_for_groups")
+    @defer.inlineCallbacks
+    def _generate_sync_entry_for_groups(self, sync_result_builder):
+        user_id = sync_result_builder.sync_config.user.to_string()
+        since_token = sync_result_builder.since_token
+        now_token = sync_result_builder.now_token
+
+        if since_token and since_token.groups_key:
+            results = yield self.store.get_groups_changes_for_user(
+                user_id, since_token.groups_key, now_token.groups_key,
+            )
+        else:
+            results = yield self.store.get_all_groups_for_user(
+                user_id, now_token.groups_key,
+            )
+
+        invited = {}
+        joined = {}
+        left = {}
+        for result in results:
+            membership = result["membership"]
+            group_id = result["group_id"]
+            gtype = result["type"]
+            content = result["content"]
+
+            if membership == "join":
+                if gtype == "membership":
+                    # TODO: Add profile
+                    content.pop("membership", None)
+                    joined[group_id] = content["content"]
+                else:
+                    joined.setdefault(group_id, {})[gtype] = content
+            elif membership == "invite":
+                if gtype == "membership":
+                    content.pop("membership", None)
+                    invited[group_id] = content["content"]
+            else:
+                if gtype == "membership":
+                    left[group_id] = content["content"]
+
+        sync_result_builder.groups = GroupsSyncResult(
+            join=joined,
+            invite=invited,
+            leave=left,
+        )
+
     @measure_func("_generate_sync_entry_for_device_list")
     @defer.inlineCallbacks
     def _generate_sync_entry_for_device_list(self, sync_result_builder,
@@ -1368,6 +1430,7 @@ class SyncResultBuilder(object):
         self.invited = []
         self.archived = []
         self.device = []
+        self.groups = None
         self.to_device = []
 
 
diff --git a/synapse/http/endpoint.py b/synapse/http/endpoint.py
index 241b17f2cb..a97532162f 100644
--- a/synapse/http/endpoint.py
+++ b/synapse/http/endpoint.py
@@ -354,16 +354,28 @@ def _get_hosts_for_srv_record(dns_client, host):
 
         return res[0]
 
-    def eb(res):
-        res.trap(DNSNameError)
-        return []
+    def eb(res, record_type):
+        if res.check(DNSNameError):
+            return []
+        logger.warn("Error looking up %s for %s: %s",
+                    record_type, host, res, res.value)
+        return res
 
     # no logcontexts here, so we can safely fire these off and gatherResults
     d1 = dns_client.lookupAddress(host).addCallbacks(cb, eb)
     d2 = dns_client.lookupIPV6Address(host).addCallbacks(cb, eb)
-    results = yield defer.gatherResults([d1, d2], consumeErrors=True)
+    results = yield defer.DeferredList(
+        [d1, d2], consumeErrors=True)
+
+    # if all of the lookups failed, raise an exception rather than blowing out
+    # the cache with an empty result.
+    if results and all(s == defer.FAILURE for (s, _) in results):
+        defer.returnValue(results[0][1])
+
+    for (success, result) in results:
+        if success == defer.FAILURE:
+            continue
 
-    for result in results:
         for answer in result:
             if not answer.payload:
                 continue
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index 747a791f83..8c8b7fa656 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -204,18 +204,15 @@ class MatrixFederationHttpClient(object):
                             raise
 
                         logger.warn(
-                            "{%s} Sending request failed to %s: %s %s: %s - %s",
+                            "{%s} Sending request failed to %s: %s %s: %s",
                             txn_id,
                             destination,
                             method,
                             url_bytes,
-                            type(e).__name__,
                             _flatten_response_never_received(e),
                         )
 
-                        log_result = "%s - %s" % (
-                            type(e).__name__, _flatten_response_never_received(e),
-                        )
+                        log_result = _flatten_response_never_received(e)
 
                         if retries_left and not timeout:
                             if long_retries:
@@ -347,7 +344,7 @@ class MatrixFederationHttpClient(object):
 
     @defer.inlineCallbacks
     def post_json(self, destination, path, data={}, long_retries=False,
-                  timeout=None, ignore_backoff=False):
+                  timeout=None, ignore_backoff=False, args={}):
         """ Sends the specifed json data using POST
 
         Args:
@@ -383,6 +380,7 @@ class MatrixFederationHttpClient(object):
             destination,
             "POST",
             path,
+            query_bytes=encode_query_args(args),
             body_callback=body_callback,
             headers_dict={"Content-Type": ["application/json"]},
             long_retries=long_retries,
@@ -427,13 +425,6 @@ class MatrixFederationHttpClient(object):
         """
         logger.debug("get_json args: %s", args)
 
-        encoded_args = {}
-        for k, vs in args.items():
-            if isinstance(vs, basestring):
-                vs = [vs]
-            encoded_args[k] = [v.encode("UTF-8") for v in vs]
-
-        query_bytes = urllib.urlencode(encoded_args, True)
         logger.debug("Query bytes: %s Retry DNS: %s", args, retry_on_dns_fail)
 
         def body_callback(method, url_bytes, headers_dict):
@@ -444,7 +435,7 @@ class MatrixFederationHttpClient(object):
             destination,
             "GET",
             path,
-            query_bytes=query_bytes,
+            query_bytes=encode_query_args(args),
             body_callback=body_callback,
             retry_on_dns_fail=retry_on_dns_fail,
             timeout=timeout,
@@ -461,6 +452,52 @@ class MatrixFederationHttpClient(object):
         defer.returnValue(json.loads(body))
 
     @defer.inlineCallbacks
+    def delete_json(self, destination, path, long_retries=False,
+                    timeout=None, ignore_backoff=False, args={}):
+        """Send a DELETE request to the remote expecting some json response
+
+        Args:
+            destination (str): The remote server to send the HTTP request
+                to.
+            path (str): The HTTP path.
+            long_retries (bool): A boolean that indicates whether we should
+                retry for a short or long time.
+            timeout(int): How long to try (in ms) the destination for before
+                giving up. None indicates no timeout.
+            ignore_backoff (bool): true to ignore the historical backoff data and
+                try the request anyway.
+        Returns:
+            Deferred: Succeeds when we get a 2xx HTTP response. The result
+            will be the decoded JSON body.
+
+            Fails with ``HTTPRequestException`` if we get an HTTP response
+            code >= 300.
+
+            Fails with ``NotRetryingDestination`` if we are not yet ready
+            to retry this server.
+        """
+
+        response = yield self._request(
+            destination,
+            "DELETE",
+            path,
+            query_bytes=encode_query_args(args),
+            headers_dict={"Content-Type": ["application/json"]},
+            long_retries=long_retries,
+            timeout=timeout,
+            ignore_backoff=ignore_backoff,
+        )
+
+        if 200 <= response.code < 300:
+            # We need to update the transactions table to say it was sent?
+            check_content_type_is_json(response.headers)
+
+        with logcontext.PreserveLoggingContext():
+            body = yield readBody(response)
+
+        defer.returnValue(json.loads(body))
+
+    @defer.inlineCallbacks
     def get_file(self, destination, path, output_stream, args={},
                  retry_on_dns_fail=True, max_size=None,
                  ignore_backoff=False):
@@ -578,12 +615,14 @@ class _JsonProducer(object):
 
 def _flatten_response_never_received(e):
     if hasattr(e, "reasons"):
-        return ", ".join(
+        reasons = ", ".join(
             _flatten_response_never_received(f.value)
             for f in e.reasons
         )
+
+        return "%s:[%s]" % (type(e).__name__, reasons)
     else:
-        return "%s: %s" % (type(e).__name__, e.message,)
+        return repr(e)
 
 
 def check_content_type_is_json(headers):
@@ -610,3 +649,15 @@ def check_content_type_is_json(headers):
         raise RuntimeError(
             "Content-Type not application/json: was '%s'" % c_type
         )
+
+
+def encode_query_args(args):
+    encoded_args = {}
+    for k, vs in args.items():
+        if isinstance(vs, basestring):
+            vs = [vs]
+        encoded_args[k] = [v.encode("UTF-8") for v in vs]
+
+    query_bytes = urllib.urlencode(encoded_args, True)
+
+    return query_bytes
diff --git a/synapse/http/server.py b/synapse/http/server.py
index 7ef3d526b1..8a27e3b422 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -145,7 +145,9 @@ def wrap_request_handler(request_handler, include_metrics=False):
                                 "error": "Internal server error",
                                 "errcode": Codes.UNKNOWN,
                             },
-                            send_cors=True
+                            send_cors=True,
+                            pretty_print=_request_user_agent_is_curl(request),
+                            version_string=self.version_string,
                         )
                     finally:
                         try:
diff --git a/synapse/push/baserules.py b/synapse/push/baserules.py
index 85effdfa46..7a18afe5f9 100644
--- a/synapse/push/baserules.py
+++ b/synapse/push/baserules.py
@@ -1,4 +1,5 @@
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2017 New Vector Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -238,6 +239,28 @@ BASE_APPEND_OVERRIDE_RULES = [
             }
         ]
     },
+    {
+        'rule_id': 'global/override/.m.rule.roomnotif',
+        'conditions': [
+            {
+                'kind': 'event_match',
+                'key': 'content.body',
+                'pattern': '@room',
+                '_id': '_roomnotif_content',
+            },
+            {
+                'kind': 'sender_notification_permission',
+                'key': 'room',
+                '_id': '_roomnotif_pl',
+            },
+        ],
+        'actions': [
+            'notify', {
+                'set_tweak': 'highlight',
+                'value': True,
+            }
+        ]
+    }
 ]
 
 
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index b0d64aa6c4..425a017bdf 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2015 OpenMarket Ltd
+# Copyright 2017 New Vector Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -19,11 +20,13 @@ from twisted.internet import defer
 
 from .push_rule_evaluator import PushRuleEvaluatorForEvent
 
+from synapse.event_auth import get_user_power_level
 from synapse.api.constants import EventTypes, Membership
 from synapse.metrics import get_metrics_for
 from synapse.util.caches import metrics as cache_metrics
 from synapse.util.caches.descriptors import cached
 from synapse.util.async import Linearizer
+from synapse.state import POWER_KEY
 
 from collections import namedtuple
 
@@ -59,6 +62,7 @@ class BulkPushRuleEvaluator(object):
     def __init__(self, hs):
         self.hs = hs
         self.store = hs.get_datastore()
+        self.auth = hs.get_auth()
 
         self.room_push_rule_cache_metrics = cache_metrics.register_cache(
             "cache",
@@ -109,6 +113,29 @@ class BulkPushRuleEvaluator(object):
         )
 
     @defer.inlineCallbacks
+    def _get_power_levels_and_sender_level(self, event, context):
+        pl_event_id = context.prev_state_ids.get(POWER_KEY)
+        if pl_event_id:
+            # fastpath: if there's a power level event, that's all we need, and
+            # not having a power level event is an extreme edge case
+            pl_event = yield self.store.get_event(pl_event_id)
+            auth_events = {POWER_KEY: pl_event}
+        else:
+            auth_events_ids = yield self.auth.compute_auth_events(
+                event, context.prev_state_ids, for_verification=False,
+            )
+            auth_events = yield self.store.get_events(auth_events_ids)
+            auth_events = {
+                (e.type, e.state_key): e for e in auth_events.itervalues()
+            }
+
+        sender_level = get_user_power_level(event.sender, auth_events)
+
+        pl_event = auth_events.get(POWER_KEY)
+
+        defer.returnValue((pl_event.content if pl_event else {}, sender_level))
+
+    @defer.inlineCallbacks
     def action_for_event_by_user(self, event, context):
         """Given an event and context, evaluate the push rules and return
         the results
@@ -123,7 +150,13 @@ class BulkPushRuleEvaluator(object):
             event, context
         )
 
-        evaluator = PushRuleEvaluatorForEvent(event, len(room_members))
+        (power_levels, sender_power_level) = (
+            yield self._get_power_levels_and_sender_level(event, context)
+        )
+
+        evaluator = PushRuleEvaluatorForEvent(
+            event, len(room_members), sender_power_level, power_levels,
+        )
 
         condition_cache = {}
 
diff --git a/synapse/push/push_rule_evaluator.py b/synapse/push/push_rule_evaluator.py
index 172c27c137..3601f2d365 100644
--- a/synapse/push/push_rule_evaluator.py
+++ b/synapse/push/push_rule_evaluator.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2017 New Vector Ltd
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -29,6 +30,21 @@ INEQUALITY_EXPR = re.compile("^([=<>]*)([0-9]*)$")
 
 
 def _room_member_count(ev, condition, room_member_count):
+    return _test_ineq_condition(condition, room_member_count)
+
+
+def _sender_notification_permission(ev, condition, sender_power_level, power_levels):
+    notif_level_key = condition.get('key')
+    if notif_level_key is None:
+        return False
+
+    notif_levels = power_levels.get('notifications', {})
+    room_notif_level = notif_levels.get(notif_level_key, 50)
+
+    return sender_power_level >= room_notif_level
+
+
+def _test_ineq_condition(condition, number):
     if 'is' not in condition:
         return False
     m = INEQUALITY_EXPR.match(condition['is'])
@@ -41,15 +57,15 @@ def _room_member_count(ev, condition, room_member_count):
     rhs = int(rhs)
 
     if ineq == '' or ineq == '==':
-        return room_member_count == rhs
+        return number == rhs
     elif ineq == '<':
-        return room_member_count < rhs
+        return number < rhs
     elif ineq == '>':
-        return room_member_count > rhs
+        return number > rhs
     elif ineq == '>=':
-        return room_member_count >= rhs
+        return number >= rhs
     elif ineq == '<=':
-        return room_member_count <= rhs
+        return number <= rhs
     else:
         return False
 
@@ -65,9 +81,11 @@ def tweaks_for_actions(actions):
 
 
 class PushRuleEvaluatorForEvent(object):
-    def __init__(self, event, room_member_count):
+    def __init__(self, event, room_member_count, sender_power_level, power_levels):
         self._event = event
         self._room_member_count = room_member_count
+        self._sender_power_level = sender_power_level
+        self._power_levels = power_levels
 
         # Maps strings of e.g. 'content.body' -> event["content"]["body"]
         self._value_cache = _flatten_dict(event)
@@ -81,6 +99,10 @@ class PushRuleEvaluatorForEvent(object):
             return _room_member_count(
                 self._event, condition, self._room_member_count
             )
+        elif condition['kind'] == 'sender_notification_permission':
+            return _sender_notification_permission(
+                self._event, condition, self._sender_power_level, self._power_levels,
+            )
         else:
             return True
 
@@ -183,7 +205,7 @@ def _glob_to_re(glob, word_boundary):
             r,
         )
         if word_boundary:
-            r = r"\b%s\b" % (r,)
+            r = _re_word_boundary(r)
 
             return re.compile(r, flags=re.IGNORECASE)
         else:
@@ -192,7 +214,7 @@ def _glob_to_re(glob, word_boundary):
             return re.compile(r, flags=re.IGNORECASE)
     elif word_boundary:
         r = re.escape(glob)
-        r = r"\b%s\b" % (r,)
+        r = _re_word_boundary(r)
 
         return re.compile(r, flags=re.IGNORECASE)
     else:
@@ -200,6 +222,18 @@ def _glob_to_re(glob, word_boundary):
         return re.compile(r, flags=re.IGNORECASE)
 
 
+def _re_word_boundary(r):
+    """
+    Adds word boundary characters to the start and end of an
+    expression to require that the match occur as a whole word,
+    but do so respecting the fact that strings starting or ending
+    with non-word characters will change word boundaries.
+    """
+    # we can't use \b as it chokes on unicode. however \W seems to be okay
+    # as shorthand for [^0-9A-Za-z_].
+    return r"(^|\W)%s(\W|$)" % (r,)
+
+
 def _flatten_dict(d, prefix=[], result=None):
     if result is None:
         result = {}
diff --git a/synapse/replication/slave/storage/groups.py b/synapse/replication/slave/storage/groups.py
new file mode 100644
index 0000000000..0bc4bce5b0
--- /dev/null
+++ b/synapse/replication/slave/storage/groups.py
@@ -0,0 +1,54 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ._base import BaseSlavedStore
+from ._slaved_id_tracker import SlavedIdTracker
+from synapse.storage import DataStore
+from synapse.util.caches.stream_change_cache import StreamChangeCache
+
+
+class SlavedGroupServerStore(BaseSlavedStore):
+    def __init__(self, db_conn, hs):
+        super(SlavedGroupServerStore, self).__init__(db_conn, hs)
+
+        self.hs = hs
+
+        self._group_updates_id_gen = SlavedIdTracker(
+            db_conn, "local_group_updates", "stream_id",
+        )
+        self._group_updates_stream_cache = StreamChangeCache(
+            "_group_updates_stream_cache", self._group_updates_id_gen.get_current_token(),
+        )
+
+    get_groups_changes_for_user = DataStore.get_groups_changes_for_user.__func__
+    get_group_stream_token = DataStore.get_group_stream_token.__func__
+    get_all_groups_for_user = DataStore.get_all_groups_for_user.__func__
+
+    def stream_positions(self):
+        result = super(SlavedGroupServerStore, self).stream_positions()
+        result["groups"] = self._group_updates_id_gen.get_current_token()
+        return result
+
+    def process_replication_rows(self, stream_name, token, rows):
+        if stream_name == "groups":
+            self._group_updates_id_gen.advance(token)
+            for row in rows:
+                self._group_updates_stream_cache.entity_has_changed(
+                    row.user_id, token
+                )
+
+        return super(SlavedGroupServerStore, self).process_replication_rows(
+            stream_name, token, rows
+        )
diff --git a/synapse/replication/tcp/resource.py b/synapse/replication/tcp/resource.py
index 3ea3ca5a6f..6c1beca4e3 100644
--- a/synapse/replication/tcp/resource.py
+++ b/synapse/replication/tcp/resource.py
@@ -160,7 +160,11 @@ class ReplicationStreamer(object):
                             "Getting stream: %s: %s -> %s",
                             stream.NAME, stream.last_token, stream.upto_token
                         )
-                        updates, current_token = yield stream.get_updates()
+                        try:
+                            updates, current_token = yield stream.get_updates()
+                        except:
+                            logger.info("Failed to handle stream %s", stream.NAME)
+                            raise
 
                         logger.debug(
                             "Sending %d updates to %d connections",
diff --git a/synapse/replication/tcp/streams.py b/synapse/replication/tcp/streams.py
index fbafe12cc2..4c60bf79f9 100644
--- a/synapse/replication/tcp/streams.py
+++ b/synapse/replication/tcp/streams.py
@@ -118,6 +118,12 @@ CurrentStateDeltaStreamRow = namedtuple("CurrentStateDeltaStream", (
     "state_key",  # str
     "event_id",  # str, optional
 ))
+GroupsStreamRow = namedtuple("GroupsStreamRow", (
+    "group_id",  # str
+    "user_id",  # str
+    "type",  # str
+    "content",  # dict
+))
 
 
 class Stream(object):
@@ -464,6 +470,19 @@ class CurrentStateDeltaStream(Stream):
         super(CurrentStateDeltaStream, self).__init__(hs)
 
 
+class GroupServerStream(Stream):
+    NAME = "groups"
+    ROW_TYPE = GroupsStreamRow
+
+    def __init__(self, hs):
+        store = hs.get_datastore()
+
+        self.current_token = store.get_group_stream_token
+        self.update_function = store.get_all_groups_changes
+
+        super(GroupServerStream, self).__init__(hs)
+
+
 STREAMS_MAP = {
     stream.NAME: stream
     for stream in (
@@ -482,5 +501,6 @@ STREAMS_MAP = {
         TagAccountDataStream,
         AccountDataStream,
         CurrentStateDeltaStream,
+        GroupServerStream,
     )
 }
diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index 3d809d181b..16f5a73b95 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -52,6 +52,7 @@ from synapse.rest.client.v2_alpha import (
     thirdparty,
     sendtodevice,
     user_directory,
+    groups,
 )
 
 from synapse.http.server import JsonResource
@@ -102,3 +103,4 @@ class ClientRestResource(JsonResource):
         thirdparty.register_servlets(hs, client_resource)
         sendtodevice.register_servlets(hs, client_resource)
         user_directory.register_servlets(hs, client_resource)
+        groups.register_servlets(hs, client_resource)
diff --git a/synapse/rest/client/v1/profile.py b/synapse/rest/client/v1/profile.py
index 1a5045c9ec..d7edc34245 100644
--- a/synapse/rest/client/v1/profile.py
+++ b/synapse/rest/client/v1/profile.py
@@ -26,13 +26,13 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
 
     def __init__(self, hs):
         super(ProfileDisplaynameRestServlet, self).__init__(hs)
-        self.handlers = hs.get_handlers()
+        self.profile_handler = hs.get_profile_handler()
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
         user = UserID.from_string(user_id)
 
-        displayname = yield self.handlers.profile_handler.get_displayname(
+        displayname = yield self.profile_handler.get_displayname(
             user,
         )
 
@@ -55,7 +55,7 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
         except:
             defer.returnValue((400, "Unable to parse name"))
 
-        yield self.handlers.profile_handler.set_displayname(
+        yield self.profile_handler.set_displayname(
             user, requester, new_name, is_admin)
 
         defer.returnValue((200, {}))
@@ -69,13 +69,13 @@ class ProfileAvatarURLRestServlet(ClientV1RestServlet):
 
     def __init__(self, hs):
         super(ProfileAvatarURLRestServlet, self).__init__(hs)
-        self.handlers = hs.get_handlers()
+        self.profile_handler = hs.get_profile_handler()
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
         user = UserID.from_string(user_id)
 
-        avatar_url = yield self.handlers.profile_handler.get_avatar_url(
+        avatar_url = yield self.profile_handler.get_avatar_url(
             user,
         )
 
@@ -97,7 +97,7 @@ class ProfileAvatarURLRestServlet(ClientV1RestServlet):
         except:
             defer.returnValue((400, "Unable to parse name"))
 
-        yield self.handlers.profile_handler.set_avatar_url(
+        yield self.profile_handler.set_avatar_url(
             user, requester, new_name, is_admin)
 
         defer.returnValue((200, {}))
@@ -111,16 +111,16 @@ class ProfileRestServlet(ClientV1RestServlet):
 
     def __init__(self, hs):
         super(ProfileRestServlet, self).__init__(hs)
-        self.handlers = hs.get_handlers()
+        self.profile_handler = hs.get_profile_handler()
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
         user = UserID.from_string(user_id)
 
-        displayname = yield self.handlers.profile_handler.get_displayname(
+        displayname = yield self.profile_handler.get_displayname(
             user,
         )
-        avatar_url = yield self.handlers.profile_handler.get_avatar_url(
+        avatar_url = yield self.profile_handler.get_avatar_url(
             user,
         )
 
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index cd388770c8..6c379d53ac 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -398,22 +398,18 @@ class JoinedRoomMemberListRestServlet(ClientV1RestServlet):
 
     def __init__(self, hs):
         super(JoinedRoomMemberListRestServlet, self).__init__(hs)
-        self.state = hs.get_state_handler()
+        self.message_handler = hs.get_handlers().message_handler
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):
-        yield self.auth.get_user_by_req(request)
+        requester = yield self.auth.get_user_by_req(request)
 
-        users_with_profile = yield self.state.get_current_user_in_room(room_id)
+        users_with_profile = yield self.message_handler.get_joined_members(
+            requester, room_id,
+        )
 
         defer.returnValue((200, {
-            "joined": {
-                user_id: {
-                    "avatar_url": profile.avatar_url,
-                    "display_name": profile.display_name,
-                }
-                for user_id, profile in users_with_profile.iteritems()
-            }
+            "joined": users_with_profile,
         }))
 
 
diff --git a/synapse/rest/client/v2_alpha/groups.py b/synapse/rest/client/v2_alpha/groups.py
new file mode 100644
index 0000000000..d11bccc1da
--- /dev/null
+++ b/synapse/rest/client/v2_alpha/groups.py
@@ -0,0 +1,717 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.internet import defer
+
+from synapse.http.servlet import RestServlet, parse_json_object_from_request
+from synapse.types import GroupID
+
+from ._base import client_v2_patterns
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class GroupServlet(RestServlet):
+    """Get the group profile
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/profile$")
+
+    def __init__(self, hs):
+        super(GroupServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        group_description = yield self.groups_handler.get_group_profile(group_id, user_id)
+
+        defer.returnValue((200, group_description))
+
+    @defer.inlineCallbacks
+    def on_POST(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        yield self.groups_handler.update_group_profile(
+            group_id, user_id, content,
+        )
+
+        defer.returnValue((200, {}))
+
+
+class GroupSummaryServlet(RestServlet):
+    """Get the full group summary
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/summary$")
+
+    def __init__(self, hs):
+        super(GroupSummaryServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        get_group_summary = yield self.groups_handler.get_group_summary(group_id, user_id)
+
+        defer.returnValue((200, get_group_summary))
+
+
+class GroupSummaryRoomsCatServlet(RestServlet):
+    """Update/delete a rooms entry in the summary.
+
+    Matches both:
+        - /groups/:group/summary/rooms/:room_id
+        - /groups/:group/summary/categories/:category/rooms/:room_id
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/summary"
+        "(/categories/(?P<category_id>[^/]+))?"
+        "/rooms/(?P<room_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSummaryRoomsCatServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, category_id, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        resp = yield self.groups_handler.update_group_summary_room(
+            group_id, user_id,
+            room_id=room_id,
+            category_id=category_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, group_id, category_id, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        resp = yield self.groups_handler.delete_group_summary_room(
+            group_id, user_id,
+            room_id=room_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class GroupCategoryServlet(RestServlet):
+    """Get/add/update/delete a group category
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/categories/(?P<category_id>[^/]+)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupCategoryServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id, category_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        category = yield self.groups_handler.get_group_category(
+            group_id, user_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue((200, category))
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, category_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        resp = yield self.groups_handler.update_group_category(
+            group_id, user_id,
+            category_id=category_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, group_id, category_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        resp = yield self.groups_handler.delete_group_category(
+            group_id, user_id,
+            category_id=category_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class GroupCategoriesServlet(RestServlet):
+    """Get all group categories
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/categories/$"
+    )
+
+    def __init__(self, hs):
+        super(GroupCategoriesServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        category = yield self.groups_handler.get_group_categories(
+            group_id, user_id,
+        )
+
+        defer.returnValue((200, category))
+
+
+class GroupRoleServlet(RestServlet):
+    """Get/add/update/delete a group role
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/roles/(?P<role_id>[^/]+)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupRoleServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id, role_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        category = yield self.groups_handler.get_group_role(
+            group_id, user_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue((200, category))
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, role_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        resp = yield self.groups_handler.update_group_role(
+            group_id, user_id,
+            role_id=role_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, group_id, role_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        resp = yield self.groups_handler.delete_group_role(
+            group_id, user_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class GroupRolesServlet(RestServlet):
+    """Get all group roles
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/roles/$"
+    )
+
+    def __init__(self, hs):
+        super(GroupRolesServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        category = yield self.groups_handler.get_group_roles(
+            group_id, user_id,
+        )
+
+        defer.returnValue((200, category))
+
+
+class GroupSummaryUsersRoleServlet(RestServlet):
+    """Update/delete a user's entry in the summary.
+
+    Matches both:
+        - /groups/:group/summary/users/:room_id
+        - /groups/:group/summary/roles/:role/users/:user_id
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/summary"
+        "(/roles/(?P<role_id>[^/]+))?"
+        "/users/(?P<user_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSummaryUsersRoleServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, role_id, user_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        resp = yield self.groups_handler.update_group_summary_user(
+            group_id, requester_user_id,
+            user_id=user_id,
+            role_id=role_id,
+            content=content,
+        )
+
+        defer.returnValue((200, resp))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, group_id, role_id, user_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        resp = yield self.groups_handler.delete_group_summary_user(
+            group_id, requester_user_id,
+            user_id=user_id,
+            role_id=role_id,
+        )
+
+        defer.returnValue((200, resp))
+
+
+class GroupRoomServlet(RestServlet):
+    """Get all rooms in a group
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/rooms$")
+
+    def __init__(self, hs):
+        super(GroupRoomServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.get_rooms_in_group(group_id, user_id)
+
+        defer.returnValue((200, result))
+
+
+class GroupUsersServlet(RestServlet):
+    """Get all users in a group
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/users$")
+
+    def __init__(self, hs):
+        super(GroupUsersServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.get_users_in_group(group_id, user_id)
+
+        defer.returnValue((200, result))
+
+
+class GroupInvitedUsersServlet(RestServlet):
+    """Get users invited to a group
+    """
+    PATTERNS = client_v2_patterns("/groups/(?P<group_id>[^/]*)/invited_users$")
+
+    def __init__(self, hs):
+        super(GroupInvitedUsersServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.get_invited_users_in_group(group_id, user_id)
+
+        defer.returnValue((200, result))
+
+
+class GroupCreateServlet(RestServlet):
+    """Create a group
+    """
+    PATTERNS = client_v2_patterns("/create_group$")
+
+    def __init__(self, hs):
+        super(GroupCreateServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+        self.server_name = hs.hostname
+
+    @defer.inlineCallbacks
+    def on_POST(self, request):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        # TODO: Create group on remote server
+        content = parse_json_object_from_request(request)
+        localpart = content.pop("localpart")
+        group_id = GroupID.create(localpart, self.server_name).to_string()
+
+        result = yield self.groups_handler.create_group(group_id, user_id, content)
+
+        defer.returnValue((200, result))
+
+
+class GroupAdminRoomsServlet(RestServlet):
+    """Add a room to the group
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/admin/rooms/(?P<room_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupAdminRoomsServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        result = yield self.groups_handler.add_room_to_group(
+            group_id, user_id, room_id, content,
+        )
+
+        defer.returnValue((200, result))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, group_id, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.remove_room_from_group(
+            group_id, user_id, room_id,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupAdminUsersInviteServlet(RestServlet):
+    """Invite a user to the group
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/admin/users/invite/(?P<user_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupAdminUsersInviteServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+        self.store = hs.get_datastore()
+        self.is_mine_id = hs.is_mine_id
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, user_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        config = content.get("config", {})
+        result = yield self.groups_handler.invite(
+            group_id, user_id, requester_user_id, config,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupAdminUsersKickServlet(RestServlet):
+    """Kick a user from the group
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/admin/users/remove/(?P<user_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(GroupAdminUsersKickServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id, user_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        result = yield self.groups_handler.remove_user_from_group(
+            group_id, user_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupSelfLeaveServlet(RestServlet):
+    """Leave a joined group
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/self/leave$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSelfLeaveServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        result = yield self.groups_handler.remove_user_from_group(
+            group_id, requester_user_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupSelfJoinServlet(RestServlet):
+    """Attempt to join a group, or knock
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/self/join$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSelfJoinServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        result = yield self.groups_handler.join_group(
+            group_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupSelfAcceptInviteServlet(RestServlet):
+    """Accept a group invite
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/self/accept_invite$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSelfAcceptInviteServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        result = yield self.groups_handler.accept_invite(
+            group_id, requester_user_id, content,
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupSelfUpdatePublicityServlet(RestServlet):
+    """Update whether we publicise a users membership of a group
+    """
+    PATTERNS = client_v2_patterns(
+        "/groups/(?P<group_id>[^/]*)/self/update_publicity$"
+    )
+
+    def __init__(self, hs):
+        super(GroupSelfUpdatePublicityServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, group_id):
+        requester = yield self.auth.get_user_by_req(request)
+        requester_user_id = requester.user.to_string()
+
+        content = parse_json_object_from_request(request)
+        publicise = content["publicise"]
+        yield self.store.update_group_publicity(
+            group_id, requester_user_id, publicise,
+        )
+
+        defer.returnValue((200, {}))
+
+
+class PublicisedGroupsForUserServlet(RestServlet):
+    """Get the list of groups a user is advertising
+    """
+    PATTERNS = client_v2_patterns(
+        "/publicised_groups/(?P<user_id>[^/]*)$"
+    )
+
+    def __init__(self, hs):
+        super(PublicisedGroupsForUserServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastore()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, user_id):
+        yield self.auth.get_user_by_req(request)
+
+        result = yield self.groups_handler.get_publicised_groups_for_user(
+            user_id
+        )
+
+        defer.returnValue((200, result))
+
+
+class PublicisedGroupsForUsersServlet(RestServlet):
+    """Get the list of groups a user is advertising
+    """
+    PATTERNS = client_v2_patterns(
+        "/publicised_groups$"
+    )
+
+    def __init__(self, hs):
+        super(PublicisedGroupsForUsersServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastore()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_POST(self, request):
+        yield self.auth.get_user_by_req(request)
+
+        content = parse_json_object_from_request(request)
+        user_ids = content["user_ids"]
+
+        result = yield self.groups_handler.bulk_get_publicised_groups(
+            user_ids
+        )
+
+        defer.returnValue((200, result))
+
+
+class GroupsForUserServlet(RestServlet):
+    """Get all groups the logged in user is joined to
+    """
+    PATTERNS = client_v2_patterns(
+        "/joined_groups$"
+    )
+
+    def __init__(self, hs):
+        super(GroupsForUserServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.groups_handler = hs.get_groups_local_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request):
+        requester = yield self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        result = yield self.groups_handler.get_joined_groups(user_id)
+
+        defer.returnValue((200, result))
+
+
+def register_servlets(hs, http_server):
+    GroupServlet(hs).register(http_server)
+    GroupSummaryServlet(hs).register(http_server)
+    GroupInvitedUsersServlet(hs).register(http_server)
+    GroupUsersServlet(hs).register(http_server)
+    GroupRoomServlet(hs).register(http_server)
+    GroupCreateServlet(hs).register(http_server)
+    GroupAdminRoomsServlet(hs).register(http_server)
+    GroupAdminUsersInviteServlet(hs).register(http_server)
+    GroupAdminUsersKickServlet(hs).register(http_server)
+    GroupSelfLeaveServlet(hs).register(http_server)
+    GroupSelfJoinServlet(hs).register(http_server)
+    GroupSelfAcceptInviteServlet(hs).register(http_server)
+    GroupsForUserServlet(hs).register(http_server)
+    GroupCategoryServlet(hs).register(http_server)
+    GroupCategoriesServlet(hs).register(http_server)
+    GroupSummaryRoomsCatServlet(hs).register(http_server)
+    GroupRoleServlet(hs).register(http_server)
+    GroupRolesServlet(hs).register(http_server)
+    GroupSelfUpdatePublicityServlet(hs).register(http_server)
+    GroupSummaryUsersRoleServlet(hs).register(http_server)
+    PublicisedGroupsForUserServlet(hs).register(http_server)
+    PublicisedGroupsForUsersServlet(hs).register(http_server)
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index 1421c18152..d9a8cdbbb5 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -17,8 +17,10 @@
 from twisted.internet import defer
 
 import synapse
+import synapse.types
 from synapse.api.auth import get_access_token_from_request, has_access_token
 from synapse.api.constants import LoginType
+from synapse.types import RoomID, RoomAlias
 from synapse.api.errors import SynapseError, Codes, UnrecognizedRequestError
 from synapse.http.servlet import (
     RestServlet, parse_json_object_from_request, assert_params_in_request, parse_string
@@ -170,6 +172,7 @@ class RegisterRestServlet(RestServlet):
         self.auth_handler = hs.get_auth_handler()
         self.registration_handler = hs.get_handlers().registration_handler
         self.identity_handler = hs.get_handlers().identity_handler
+        self.room_member_handler = hs.get_handlers().room_member_handler
         self.device_handler = hs.get_device_handler()
         self.macaroon_gen = hs.get_macaroon_generator()
 
@@ -340,6 +343,14 @@ class RegisterRestServlet(RestServlet):
                 generate_token=False,
             )
 
+            # auto-join the user to any rooms we're supposed to dump them into
+            fake_requester = synapse.types.create_requester(registered_user_id)
+            for r in self.hs.config.auto_join_rooms:
+                try:
+                    yield self._join_user_to_room(fake_requester, r)
+                except Exception as e:
+                    logger.error("Failed to join new user to %r: %r", r, e)
+
             # remember that we've now registered that user account, and with
             #  what user ID (since the user may not have specified)
             self.auth_handler.set_session_data(
@@ -373,6 +384,29 @@ class RegisterRestServlet(RestServlet):
         return 200, {}
 
     @defer.inlineCallbacks
+    def _join_user_to_room(self, requester, room_identifier):
+        room_id = None
+        if RoomID.is_valid(room_identifier):
+            room_id = room_identifier
+        elif RoomAlias.is_valid(room_identifier):
+            room_alias = RoomAlias.from_string(room_identifier)
+            room_id, remote_room_hosts = (
+                yield self.room_member_handler.lookup_room_alias(room_alias)
+            )
+            room_id = room_id.to_string()
+        else:
+            raise SynapseError(400, "%s was not legal room ID or room alias" % (
+                room_identifier,
+            ))
+
+        yield self.room_member_handler.update_membership(
+            requester=requester,
+            target=requester.user,
+            room_id=room_id,
+            action="join",
+        )
+
+    @defer.inlineCallbacks
     def _do_appservice_registration(self, username, as_token, body):
         user_id = yield self.registration_handler.appservice_register(
             username, as_token
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 978af9c280..a1e0e53b33 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -200,6 +200,11 @@ class SyncRestServlet(RestServlet):
                 "invite": invited,
                 "leave": archived,
             },
+            "groups": {
+                "join": sync_result.groups.join,
+                "invite": sync_result.groups.invite,
+                "leave": sync_result.groups.leave,
+            },
             "device_one_time_keys_count": sync_result.device_one_time_keys_count,
             "next_batch": sync_result.next_batch.to_string(),
         }
diff --git a/synapse/rest/media/v1/filepath.py b/synapse/rest/media/v1/filepath.py
index d92b7ff337..d5164e47e0 100644
--- a/synapse/rest/media/v1/filepath.py
+++ b/synapse/rest/media/v1/filepath.py
@@ -14,78 +14,200 @@
 # limitations under the License.
 
 import os
+import re
+import functools
+
+NEW_FORMAT_ID_RE = re.compile(r"^\d\d\d\d-\d\d-\d\d")
+
+
+def _wrap_in_base_path(func):
+    """Takes a function that returns a relative path and turns it into an
+    absolute path based on the location of the primary media store
+    """
+    @functools.wraps(func)
+    def _wrapped(self, *args, **kwargs):
+        path = func(self, *args, **kwargs)
+        return os.path.join(self.base_path, path)
+
+    return _wrapped
 
 
 class MediaFilePaths(object):
+    """Describes where files are stored on disk.
 
-    def __init__(self, base_path):
-        self.base_path = base_path
+    Most of the functions have a `*_rel` variant which returns a file path that
+    is relative to the base media store path. This is mainly used when we want
+    to write to the backup media store (when one is configured)
+    """
 
-    def default_thumbnail(self, default_top_level, default_sub_type, width,
-                          height, content_type, method):
+    def __init__(self, primary_base_path):
+        self.base_path = primary_base_path
+
+    def default_thumbnail_rel(self, default_top_level, default_sub_type, width,
+                              height, content_type, method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s-%s" % (
             width, height, top_level_type, sub_type, method
         )
         return os.path.join(
-            self.base_path, "default_thumbnails", default_top_level,
+            "default_thumbnails", default_top_level,
             default_sub_type, file_name
         )
 
-    def local_media_filepath(self, media_id):
+    default_thumbnail = _wrap_in_base_path(default_thumbnail_rel)
+
+    def local_media_filepath_rel(self, media_id):
         return os.path.join(
-            self.base_path, "local_content",
+            "local_content",
             media_id[0:2], media_id[2:4], media_id[4:]
         )
 
-    def local_media_thumbnail(self, media_id, width, height, content_type,
-                              method):
+    local_media_filepath = _wrap_in_base_path(local_media_filepath_rel)
+
+    def local_media_thumbnail_rel(self, media_id, width, height, content_type,
+                                  method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s-%s" % (
             width, height, top_level_type, sub_type, method
         )
         return os.path.join(
-            self.base_path, "local_thumbnails",
+            "local_thumbnails",
             media_id[0:2], media_id[2:4], media_id[4:],
             file_name
         )
 
-    def remote_media_filepath(self, server_name, file_id):
+    local_media_thumbnail = _wrap_in_base_path(local_media_thumbnail_rel)
+
+    def remote_media_filepath_rel(self, server_name, file_id):
         return os.path.join(
-            self.base_path, "remote_content", server_name,
+            "remote_content", server_name,
             file_id[0:2], file_id[2:4], file_id[4:]
         )
 
-    def remote_media_thumbnail(self, server_name, file_id, width, height,
-                               content_type, method):
+    remote_media_filepath = _wrap_in_base_path(remote_media_filepath_rel)
+
+    def remote_media_thumbnail_rel(self, server_name, file_id, width, height,
+                                   content_type, method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s" % (width, height, top_level_type, sub_type)
         return os.path.join(
-            self.base_path, "remote_thumbnail", server_name,
+            "remote_thumbnail", server_name,
             file_id[0:2], file_id[2:4], file_id[4:],
             file_name
         )
 
+    remote_media_thumbnail = _wrap_in_base_path(remote_media_thumbnail_rel)
+
     def remote_media_thumbnail_dir(self, server_name, file_id):
         return os.path.join(
             self.base_path, "remote_thumbnail", server_name,
             file_id[0:2], file_id[2:4], file_id[4:],
         )
 
-    def url_cache_filepath(self, media_id):
-        return os.path.join(
-            self.base_path, "url_cache",
-            media_id[0:2], media_id[2:4], media_id[4:]
-        )
+    def url_cache_filepath_rel(self, media_id):
+        if NEW_FORMAT_ID_RE.match(media_id):
+            # Media id is of the form <DATE><RANDOM_STRING>
+            # E.g.: 2017-09-28-fsdRDt24DS234dsf
+            return os.path.join(
+                "url_cache",
+                media_id[:10], media_id[11:]
+            )
+        else:
+            return os.path.join(
+                "url_cache",
+                media_id[0:2], media_id[2:4], media_id[4:],
+            )
+
+    url_cache_filepath = _wrap_in_base_path(url_cache_filepath_rel)
+
+    def url_cache_filepath_dirs_to_delete(self, media_id):
+        "The dirs to try and remove if we delete the media_id file"
+        if NEW_FORMAT_ID_RE.match(media_id):
+            return [
+                os.path.join(
+                    self.base_path, "url_cache",
+                    media_id[:10],
+                ),
+            ]
+        else:
+            return [
+                os.path.join(
+                    self.base_path, "url_cache",
+                    media_id[0:2], media_id[2:4],
+                ),
+                os.path.join(
+                    self.base_path, "url_cache",
+                    media_id[0:2],
+                ),
+            ]
+
+    def url_cache_thumbnail_rel(self, media_id, width, height, content_type,
+                                method):
+        # Media id is of the form <DATE><RANDOM_STRING>
+        # E.g.: 2017-09-28-fsdRDt24DS234dsf
 
-    def url_cache_thumbnail(self, media_id, width, height, content_type,
-                            method):
         top_level_type, sub_type = content_type.split("/")
         file_name = "%i-%i-%s-%s-%s" % (
             width, height, top_level_type, sub_type, method
         )
-        return os.path.join(
-            self.base_path, "url_cache_thumbnails",
-            media_id[0:2], media_id[2:4], media_id[4:],
-            file_name
-        )
+
+        if NEW_FORMAT_ID_RE.match(media_id):
+            return os.path.join(
+                "url_cache_thumbnails",
+                media_id[:10], media_id[11:],
+                file_name
+            )
+        else:
+            return os.path.join(
+                "url_cache_thumbnails",
+                media_id[0:2], media_id[2:4], media_id[4:],
+                file_name
+            )
+
+    url_cache_thumbnail = _wrap_in_base_path(url_cache_thumbnail_rel)
+
+    def url_cache_thumbnail_directory(self, media_id):
+        # Media id is of the form <DATE><RANDOM_STRING>
+        # E.g.: 2017-09-28-fsdRDt24DS234dsf
+
+        if NEW_FORMAT_ID_RE.match(media_id):
+            return os.path.join(
+                self.base_path, "url_cache_thumbnails",
+                media_id[:10], media_id[11:],
+            )
+        else:
+            return os.path.join(
+                self.base_path, "url_cache_thumbnails",
+                media_id[0:2], media_id[2:4], media_id[4:],
+            )
+
+    def url_cache_thumbnail_dirs_to_delete(self, media_id):
+        "The dirs to try and remove if we delete the media_id thumbnails"
+        # Media id is of the form <DATE><RANDOM_STRING>
+        # E.g.: 2017-09-28-fsdRDt24DS234dsf
+        if NEW_FORMAT_ID_RE.match(media_id):
+            return [
+                os.path.join(
+                    self.base_path, "url_cache_thumbnails",
+                    media_id[:10], media_id[11:],
+                ),
+                os.path.join(
+                    self.base_path, "url_cache_thumbnails",
+                    media_id[:10],
+                ),
+            ]
+        else:
+            return [
+                os.path.join(
+                    self.base_path, "url_cache_thumbnails",
+                    media_id[0:2], media_id[2:4], media_id[4:],
+                ),
+                os.path.join(
+                    self.base_path, "url_cache_thumbnails",
+                    media_id[0:2], media_id[2:4],
+                ),
+                os.path.join(
+                    self.base_path, "url_cache_thumbnails",
+                    media_id[0:2],
+                ),
+            ]
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 0ea1248ce6..6b50b45b1f 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -33,7 +33,7 @@ from synapse.api.errors import SynapseError, HttpResponseException, \
 
 from synapse.util.async import Linearizer
 from synapse.util.stringutils import is_ascii
-from synapse.util.logcontext import preserve_context_over_fn
+from synapse.util.logcontext import make_deferred_yieldable, preserve_fn
 from synapse.util.retryutils import NotRetryingDestination
 
 import os
@@ -59,7 +59,14 @@ class MediaRepository(object):
         self.store = hs.get_datastore()
         self.max_upload_size = hs.config.max_upload_size
         self.max_image_pixels = hs.config.max_image_pixels
-        self.filepaths = MediaFilePaths(hs.config.media_store_path)
+
+        self.primary_base_path = hs.config.media_store_path
+        self.filepaths = MediaFilePaths(self.primary_base_path)
+
+        self.backup_base_path = hs.config.backup_media_store_path
+
+        self.synchronous_backup_media_store = hs.config.synchronous_backup_media_store
+
         self.dynamic_thumbnails = hs.config.dynamic_thumbnails
         self.thumbnail_requirements = hs.config.thumbnail_requirements
 
@@ -87,18 +94,86 @@ class MediaRepository(object):
         if not os.path.exists(dirname):
             os.makedirs(dirname)
 
+    @staticmethod
+    def _write_file_synchronously(source, fname):
+        """Write `source` to the path `fname` synchronously. Should be called
+        from a thread.
+
+        Args:
+            source: A file like object to be written
+            fname (str): Path to write to
+        """
+        MediaRepository._makedirs(fname)
+        source.seek(0)  # Ensure we read from the start of the file
+        with open(fname, "wb") as f:
+            shutil.copyfileobj(source, f)
+
+    @defer.inlineCallbacks
+    def write_to_file_and_backup(self, source, path):
+        """Write `source` to the on disk media store, and also the backup store
+        if configured.
+
+        Args:
+            source: A file like object that should be written
+            path (str): Relative path to write file to
+
+        Returns:
+            Deferred[str]: the file path written to in the primary media store
+        """
+        fname = os.path.join(self.primary_base_path, path)
+
+        # Write to the main repository
+        yield make_deferred_yieldable(threads.deferToThread(
+            self._write_file_synchronously, source, fname,
+        ))
+
+        # Write to backup repository
+        yield self.copy_to_backup(path)
+
+        defer.returnValue(fname)
+
+    @defer.inlineCallbacks
+    def copy_to_backup(self, path):
+        """Copy a file from the primary to backup media store, if configured.
+
+        Args:
+            path(str): Relative path to write file to
+        """
+        if self.backup_base_path:
+            primary_fname = os.path.join(self.primary_base_path, path)
+            backup_fname = os.path.join(self.backup_base_path, path)
+
+            # We can either wait for successful writing to the backup repository
+            # or write in the background and immediately return
+            if self.synchronous_backup_media_store:
+                yield make_deferred_yieldable(threads.deferToThread(
+                    shutil.copyfile, primary_fname, backup_fname,
+                ))
+            else:
+                preserve_fn(threads.deferToThread)(
+                    shutil.copyfile, primary_fname, backup_fname,
+                )
+
     @defer.inlineCallbacks
     def create_content(self, media_type, upload_name, content, content_length,
                        auth_user):
+        """Store uploaded content for a local user and return the mxc URL
+
+        Args:
+            media_type(str): The content type of the file
+            upload_name(str): The name of the file
+            content: A file like object that is the content to store
+            content_length(int): The length of the content
+            auth_user(str): The user_id of the uploader
+
+        Returns:
+            Deferred[str]: The mxc url of the stored content
+        """
         media_id = random_string(24)
 
-        fname = self.filepaths.local_media_filepath(media_id)
-        self._makedirs(fname)
-
-        # This shouldn't block for very long because the content will have
-        # already been uploaded at this point.
-        with open(fname, "wb") as f:
-            f.write(content)
+        fname = yield self.write_to_file_and_backup(
+            content, self.filepaths.local_media_filepath_rel(media_id)
+        )
 
         logger.info("Stored local media in file %r", fname)
 
@@ -115,7 +190,7 @@ class MediaRepository(object):
             "media_length": content_length,
         }
 
-        yield self._generate_local_thumbnails(media_id, media_info)
+        yield self._generate_thumbnails(None, media_id, media_info)
 
         defer.returnValue("mxc://%s/%s" % (self.server_name, media_id))
 
@@ -148,9 +223,10 @@ class MediaRepository(object):
     def _download_remote_file(self, server_name, media_id):
         file_id = random_string(24)
 
-        fname = self.filepaths.remote_media_filepath(
+        fpath = self.filepaths.remote_media_filepath_rel(
             server_name, file_id
         )
+        fname = os.path.join(self.primary_base_path, fpath)
         self._makedirs(fname)
 
         try:
@@ -192,6 +268,8 @@ class MediaRepository(object):
                                      server_name, media_id)
                     raise SynapseError(502, "Failed to fetch remote media")
 
+            yield self.copy_to_backup(fpath)
+
             media_type = headers["Content-Type"][0]
             time_now_ms = self.clock.time_msec()
 
@@ -244,7 +322,7 @@ class MediaRepository(object):
             "filesystem_id": file_id,
         }
 
-        yield self._generate_remote_thumbnails(
+        yield self._generate_thumbnails(
             server_name, media_id, media_info
         )
 
@@ -253,9 +331,8 @@ class MediaRepository(object):
     def _get_thumbnail_requirements(self, media_type):
         return self.thumbnail_requirements.get(media_type, ())
 
-    def _generate_thumbnail(self, input_path, t_path, t_width, t_height,
+    def _generate_thumbnail(self, thumbnailer, t_width, t_height,
                             t_method, t_type):
-        thumbnailer = Thumbnailer(input_path)
         m_width = thumbnailer.width
         m_height = thumbnailer.height
 
@@ -267,72 +344,105 @@ class MediaRepository(object):
             return
 
         if t_method == "crop":
-            t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
+            t_byte_source = thumbnailer.crop(t_width, t_height, t_type)
         elif t_method == "scale":
             t_width, t_height = thumbnailer.aspect(t_width, t_height)
             t_width = min(m_width, t_width)
             t_height = min(m_height, t_height)
-            t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
+            t_byte_source = thumbnailer.scale(t_width, t_height, t_type)
         else:
-            t_len = None
+            t_byte_source = None
 
-        return t_len
+        return t_byte_source
 
     @defer.inlineCallbacks
     def generate_local_exact_thumbnail(self, media_id, t_width, t_height,
                                        t_method, t_type):
         input_path = self.filepaths.local_media_filepath(media_id)
 
-        t_path = self.filepaths.local_media_thumbnail(
-            media_id, t_width, t_height, t_type, t_method
-        )
-        self._makedirs(t_path)
-
-        t_len = yield preserve_context_over_fn(
-            threads.deferToThread,
+        thumbnailer = Thumbnailer(input_path)
+        t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
             self._generate_thumbnail,
-            input_path, t_path, t_width, t_height, t_method, t_type
-        )
+            thumbnailer, t_width, t_height, t_method, t_type
+        ))
+
+        if t_byte_source:
+            try:
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source,
+                    self.filepaths.local_media_thumbnail_rel(
+                        media_id, t_width, t_height, t_type, t_method
+                    )
+                )
+            finally:
+                t_byte_source.close()
+
+            logger.info("Stored thumbnail in file %r", output_path)
+
+            t_len = os.path.getsize(output_path)
 
-        if t_len:
             yield self.store.store_local_thumbnail(
                 media_id, t_width, t_height, t_type, t_method, t_len
             )
 
-            defer.returnValue(t_path)
+            defer.returnValue(output_path)
 
     @defer.inlineCallbacks
     def generate_remote_exact_thumbnail(self, server_name, file_id, media_id,
                                         t_width, t_height, t_method, t_type):
         input_path = self.filepaths.remote_media_filepath(server_name, file_id)
 
-        t_path = self.filepaths.remote_media_thumbnail(
-            server_name, file_id, t_width, t_height, t_type, t_method
-        )
-        self._makedirs(t_path)
-
-        t_len = yield preserve_context_over_fn(
-            threads.deferToThread,
+        thumbnailer = Thumbnailer(input_path)
+        t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
             self._generate_thumbnail,
-            input_path, t_path, t_width, t_height, t_method, t_type
-        )
+            thumbnailer, t_width, t_height, t_method, t_type
+        ))
+
+        if t_byte_source:
+            try:
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source,
+                    self.filepaths.remote_media_thumbnail_rel(
+                        server_name, file_id, t_width, t_height, t_type, t_method
+                    )
+                )
+            finally:
+                t_byte_source.close()
+
+            logger.info("Stored thumbnail in file %r", output_path)
+
+            t_len = os.path.getsize(output_path)
 
-        if t_len:
             yield self.store.store_remote_media_thumbnail(
                 server_name, media_id, file_id,
                 t_width, t_height, t_type, t_method, t_len
             )
 
-            defer.returnValue(t_path)
+            defer.returnValue(output_path)
 
     @defer.inlineCallbacks
-    def _generate_local_thumbnails(self, media_id, media_info, url_cache=False):
+    def _generate_thumbnails(self, server_name, media_id, media_info, url_cache=False):
+        """Generate and store thumbnails for an image.
+
+        Args:
+            server_name(str|None): The server name if remote media, else None if local
+            media_id(str)
+            media_info(dict)
+            url_cache(bool): If we are thumbnailing images downloaded for the URL cache,
+                used exclusively by the url previewer
+
+        Returns:
+            Deferred[dict]: Dict with "width" and "height" keys of original image
+        """
         media_type = media_info["media_type"]
+        file_id = media_info.get("filesystem_id")
         requirements = self._get_thumbnail_requirements(media_type)
         if not requirements:
             return
 
-        if url_cache:
+        if server_name:
+            input_path = self.filepaths.remote_media_filepath(server_name, file_id)
+        elif url_cache:
             input_path = self.filepaths.url_cache_filepath(media_id)
         else:
             input_path = self.filepaths.local_media_filepath(media_id)
@@ -348,135 +458,72 @@ class MediaRepository(object):
             )
             return
 
-        local_thumbnails = []
-
-        def generate_thumbnails():
-            scales = set()
-            crops = set()
-            for r_width, r_height, r_method, r_type in requirements:
-                if r_method == "scale":
-                    t_width, t_height = thumbnailer.aspect(r_width, r_height)
-                    scales.add((
-                        min(m_width, t_width), min(m_height, t_height), r_type,
-                    ))
-                elif r_method == "crop":
-                    crops.add((r_width, r_height, r_type))
-
-            for t_width, t_height, t_type in scales:
-                t_method = "scale"
-                if url_cache:
-                    t_path = self.filepaths.url_cache_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                else:
-                    t_path = self.filepaths.local_media_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                self._makedirs(t_path)
-                t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
+        # We deduplicate the thumbnail sizes by ignoring the cropped versions if
+        # they have the same dimensions of a scaled one.
+        thumbnails = {}
+        for r_width, r_height, r_method, r_type in requirements:
+            if r_method == "crop":
+                thumbnails.setdefault((r_width, r_height, r_type), r_method)
+            elif r_method == "scale":
+                t_width, t_height = thumbnailer.aspect(r_width, r_height)
+                t_width = min(m_width, t_width)
+                t_height = min(m_height, t_height)
+                thumbnails[(t_width, t_height, r_type)] = r_method
+
+        # Now we generate the thumbnails for each dimension, store it
+        for (t_width, t_height, t_type), t_method in thumbnails.iteritems():
+            # Work out the correct file name for thumbnail
+            if server_name:
+                file_path = self.filepaths.remote_media_thumbnail_rel(
+                    server_name, file_id, t_width, t_height, t_type, t_method
+                )
+            elif url_cache:
+                file_path = self.filepaths.url_cache_thumbnail_rel(
+                    media_id, t_width, t_height, t_type, t_method
+                )
+            else:
+                file_path = self.filepaths.local_media_thumbnail_rel(
+                    media_id, t_width, t_height, t_type, t_method
+                )
 
-                local_thumbnails.append((
-                    media_id, t_width, t_height, t_type, t_method, t_len
+            # Generate the thumbnail
+            if t_method == "crop":
+                t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
+                    thumbnailer.crop,
+                    t_width, t_height, t_type,
                 ))
-
-            for t_width, t_height, t_type in crops:
-                if (t_width, t_height, t_type) in scales:
-                    # If the aspect ratio of the cropped thumbnail matches a purely
-                    # scaled one then there is no point in calculating a separate
-                    # thumbnail.
-                    continue
-                t_method = "crop"
-                if url_cache:
-                    t_path = self.filepaths.url_cache_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                else:
-                    t_path = self.filepaths.local_media_thumbnail(
-                        media_id, t_width, t_height, t_type, t_method
-                    )
-                self._makedirs(t_path)
-                t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
-                local_thumbnails.append((
-                    media_id, t_width, t_height, t_type, t_method, t_len
+            elif t_method == "scale":
+                t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
+                    thumbnailer.scale,
+                    t_width, t_height, t_type,
                 ))
+            else:
+                logger.error("Unrecognized method: %r", t_method)
+                continue
 
-        yield preserve_context_over_fn(threads.deferToThread, generate_thumbnails)
-
-        for l in local_thumbnails:
-            yield self.store.store_local_thumbnail(*l)
-
-        defer.returnValue({
-            "width": m_width,
-            "height": m_height,
-        })
-
-    @defer.inlineCallbacks
-    def _generate_remote_thumbnails(self, server_name, media_id, media_info):
-        media_type = media_info["media_type"]
-        file_id = media_info["filesystem_id"]
-        requirements = self._get_thumbnail_requirements(media_type)
-        if not requirements:
-            return
+            if not t_byte_source:
+                continue
 
-        remote_thumbnails = []
+            try:
+                # Write to disk
+                output_path = yield self.write_to_file_and_backup(
+                    t_byte_source, file_path,
+                )
+            finally:
+                t_byte_source.close()
 
-        input_path = self.filepaths.remote_media_filepath(server_name, file_id)
-        thumbnailer = Thumbnailer(input_path)
-        m_width = thumbnailer.width
-        m_height = thumbnailer.height
+            t_len = os.path.getsize(output_path)
 
-        def generate_thumbnails():
-            if m_width * m_height >= self.max_image_pixels:
-                logger.info(
-                    "Image too large to thumbnail %r x %r > %r",
-                    m_width, m_height, self.max_image_pixels
-                )
-                return
-
-            scales = set()
-            crops = set()
-            for r_width, r_height, r_method, r_type in requirements:
-                if r_method == "scale":
-                    t_width, t_height = thumbnailer.aspect(r_width, r_height)
-                    scales.add((
-                        min(m_width, t_width), min(m_height, t_height), r_type,
-                    ))
-                elif r_method == "crop":
-                    crops.add((r_width, r_height, r_type))
-
-            for t_width, t_height, t_type in scales:
-                t_method = "scale"
-                t_path = self.filepaths.remote_media_thumbnail(
-                    server_name, file_id, t_width, t_height, t_type, t_method
-                )
-                self._makedirs(t_path)
-                t_len = thumbnailer.scale(t_path, t_width, t_height, t_type)
-                remote_thumbnails.append([
+            # Write to database
+            if server_name:
+                yield self.store.store_remote_media_thumbnail(
                     server_name, media_id, file_id,
                     t_width, t_height, t_type, t_method, t_len
-                ])
-
-            for t_width, t_height, t_type in crops:
-                if (t_width, t_height, t_type) in scales:
-                    # If the aspect ratio of the cropped thumbnail matches a purely
-                    # scaled one then there is no point in calculating a separate
-                    # thumbnail.
-                    continue
-                t_method = "crop"
-                t_path = self.filepaths.remote_media_thumbnail(
-                    server_name, file_id, t_width, t_height, t_type, t_method
                 )
-                self._makedirs(t_path)
-                t_len = thumbnailer.crop(t_path, t_width, t_height, t_type)
-                remote_thumbnails.append([
-                    server_name, media_id, file_id,
-                    t_width, t_height, t_type, t_method, t_len
-                ])
-
-        yield preserve_context_over_fn(threads.deferToThread, generate_thumbnails)
-
-        for r in remote_thumbnails:
-            yield self.store.store_remote_media_thumbnail(*r)
+            else:
+                yield self.store.store_local_thumbnail(
+                    media_id, t_width, t_height, t_type, t_method, t_len
+                )
 
         defer.returnValue({
             "width": m_width,
@@ -497,6 +544,8 @@ class MediaRepository(object):
 
             logger.info("Deleting: %r", key)
 
+            # TODO: Should we delete from the backup store
+
             with (yield self.remote_media_linearizer.queue(key)):
                 full_path = self.filepaths.remote_media_filepath(origin, file_id)
                 try:
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index b81a336c5d..2a3e37fdf4 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -36,6 +36,9 @@ import cgi
 import ujson as json
 import urlparse
 import itertools
+import datetime
+import errno
+import shutil
 
 import logging
 logger = logging.getLogger(__name__)
@@ -56,6 +59,7 @@ class PreviewUrlResource(Resource):
         self.store = hs.get_datastore()
         self.client = SpiderHttpClient(hs)
         self.media_repo = media_repo
+        self.primary_base_path = media_repo.primary_base_path
 
         self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist
 
@@ -70,6 +74,10 @@ class PreviewUrlResource(Resource):
 
         self.downloads = {}
 
+        self._cleaner_loop = self.clock.looping_call(
+            self._expire_url_cache_data, 10 * 1000
+        )
+
     def render_GET(self, request):
         self._async_render_GET(request)
         return NOT_DONE_YET
@@ -130,7 +138,7 @@ class PreviewUrlResource(Resource):
         cache_result = yield self.store.get_url_cache(url, ts)
         if (
             cache_result and
-            cache_result["download_ts"] + cache_result["expires"] > ts and
+            cache_result["expires_ts"] > ts and
             cache_result["response_code"] / 100 == 2
         ):
             respond_with_json_bytes(
@@ -163,8 +171,8 @@ class PreviewUrlResource(Resource):
         logger.debug("got media_info of '%s'" % media_info)
 
         if _is_media(media_info['media_type']):
-            dims = yield self.media_repo._generate_local_thumbnails(
-                media_info['filesystem_id'], media_info, url_cache=True,
+            dims = yield self.media_repo._generate_thumbnails(
+                None, media_info['filesystem_id'], media_info, url_cache=True,
             )
 
             og = {
@@ -209,8 +217,8 @@ class PreviewUrlResource(Resource):
 
                 if _is_media(image_info['media_type']):
                     # TODO: make sure we don't choke on white-on-transparent images
-                    dims = yield self.media_repo._generate_local_thumbnails(
-                        image_info['filesystem_id'], image_info, url_cache=True,
+                    dims = yield self.media_repo._generate_thumbnails(
+                        None, image_info['filesystem_id'], image_info, url_cache=True,
                     )
                     if dims:
                         og["og:image:width"] = dims['width']
@@ -239,7 +247,7 @@ class PreviewUrlResource(Resource):
             url,
             media_info["response_code"],
             media_info["etag"],
-            media_info["expires"],
+            media_info["expires"] + media_info["created_ts"],
             json.dumps(og),
             media_info["filesystem_id"],
             media_info["created_ts"],
@@ -253,10 +261,10 @@ class PreviewUrlResource(Resource):
         # we're most likely being explicitly triggered by a human rather than a
         # bot, so are we really a robot?
 
-        # XXX: horrible duplication with base_resource's _download_remote_file()
-        file_id = random_string(24)
+        file_id = datetime.date.today().isoformat() + '_' + random_string(16)
 
-        fname = self.filepaths.url_cache_filepath(file_id)
+        fpath = self.filepaths.url_cache_filepath_rel(file_id)
+        fname = os.path.join(self.primary_base_path, fpath)
         self.media_repo._makedirs(fname)
 
         try:
@@ -267,6 +275,8 @@ class PreviewUrlResource(Resource):
                 )
                 # FIXME: pass through 404s and other error messages nicely
 
+            yield self.media_repo.copy_to_backup(fpath)
+
             media_type = headers["Content-Type"][0]
             time_now_ms = self.clock.time_msec()
 
@@ -328,6 +338,91 @@ class PreviewUrlResource(Resource):
             "etag": headers["ETag"][0] if "ETag" in headers else None,
         })
 
+    @defer.inlineCallbacks
+    def _expire_url_cache_data(self):
+        """Clean up expired url cache content, media and thumbnails.
+        """
+
+        # TODO: Delete from backup media store
+
+        now = self.clock.time_msec()
+
+        # First we delete expired url cache entries
+        media_ids = yield self.store.get_expired_url_cache(now)
+
+        removed_media = []
+        for media_id in media_ids:
+            fname = self.filepaths.url_cache_filepath(media_id)
+            try:
+                os.remove(fname)
+            except OSError as e:
+                # If the path doesn't exist, meh
+                if e.errno != errno.ENOENT:
+                    logger.warn("Failed to remove media: %r: %s", media_id, e)
+                    continue
+
+            removed_media.append(media_id)
+
+            try:
+                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
+                for dir in dirs:
+                    os.rmdir(dir)
+            except:
+                pass
+
+        yield self.store.delete_url_cache(removed_media)
+
+        if removed_media:
+            logger.info("Deleted %d entries from url cache", len(removed_media))
+
+        # Now we delete old images associated with the url cache.
+        # These may be cached for a bit on the client (i.e., they
+        # may have a room open with a preview url thing open).
+        # So we wait a couple of days before deleting, just in case.
+        expire_before = now - 2 * 24 * 60 * 60 * 1000
+        media_ids = yield self.store.get_url_cache_media_before(expire_before)
+
+        removed_media = []
+        for media_id in media_ids:
+            fname = self.filepaths.url_cache_filepath(media_id)
+            try:
+                os.remove(fname)
+            except OSError as e:
+                # If the path doesn't exist, meh
+                if e.errno != errno.ENOENT:
+                    logger.warn("Failed to remove media: %r: %s", media_id, e)
+                    continue
+
+            try:
+                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
+                for dir in dirs:
+                    os.rmdir(dir)
+            except:
+                pass
+
+            thumbnail_dir = self.filepaths.url_cache_thumbnail_directory(media_id)
+            try:
+                shutil.rmtree(thumbnail_dir)
+            except OSError as e:
+                # If the path doesn't exist, meh
+                if e.errno != errno.ENOENT:
+                    logger.warn("Failed to remove media: %r: %s", media_id, e)
+                    continue
+
+            removed_media.append(media_id)
+
+            try:
+                dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id)
+                for dir in dirs:
+                    os.rmdir(dir)
+            except:
+                pass
+
+        yield self.store.delete_url_cache_media(removed_media)
+
+        if removed_media:
+            logger.info("Deleted %d media from url cache", len(removed_media))
+
 
 def decode_and_calc_og(body, media_uri, request_encoding=None):
     from lxml import etree
diff --git a/synapse/rest/media/v1/thumbnailer.py b/synapse/rest/media/v1/thumbnailer.py
index 3868d4f65f..e1ee535b9a 100644
--- a/synapse/rest/media/v1/thumbnailer.py
+++ b/synapse/rest/media/v1/thumbnailer.py
@@ -50,12 +50,16 @@ class Thumbnailer(object):
         else:
             return ((max_height * self.width) // self.height, max_height)
 
-    def scale(self, output_path, width, height, output_type):
-        """Rescales the image to the given dimensions"""
+    def scale(self, width, height, output_type):
+        """Rescales the image to the given dimensions.
+
+        Returns:
+            BytesIO: the bytes of the encoded image ready to be written to disk
+        """
         scaled = self.image.resize((width, height), Image.ANTIALIAS)
-        return self.save_image(scaled, output_type, output_path)
+        return self._encode_image(scaled, output_type)
 
-    def crop(self, output_path, width, height, output_type):
+    def crop(self, width, height, output_type):
         """Rescales and crops the image to the given dimensions preserving
         aspect::
             (w_in / h_in) = (w_scaled / h_scaled)
@@ -65,6 +69,9 @@ class Thumbnailer(object):
         Args:
             max_width: The largest possible width.
             max_height: The larget possible height.
+
+        Returns:
+            BytesIO: the bytes of the encoded image ready to be written to disk
         """
         if width * self.height > height * self.width:
             scaled_height = (width * self.height) // self.width
@@ -82,13 +89,9 @@ class Thumbnailer(object):
             crop_left = (scaled_width - width) // 2
             crop_right = width + crop_left
             cropped = scaled_image.crop((crop_left, 0, crop_right, height))
-        return self.save_image(cropped, output_type, output_path)
+        return self._encode_image(cropped, output_type)
 
-    def save_image(self, output_image, output_type, output_path):
+    def _encode_image(self, output_image, output_type):
         output_bytes_io = BytesIO()
         output_image.save(output_bytes_io, self.FORMATS[output_type], quality=80)
-        output_bytes = output_bytes_io.getvalue()
-        with open(output_path, "wb") as output_file:
-            output_file.write(output_bytes)
-        logger.info("Stored thumbnail in file %r", output_path)
-        return len(output_bytes)
+        return output_bytes_io
diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index 4ab33f73bf..f6f498cdc5 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -93,7 +93,7 @@ class UploadResource(Resource):
         # TODO(markjh): parse content-dispostion
 
         content_uri = yield self.media_repo.create_content(
-            media_type, upload_name, request.content.read(),
+            media_type, upload_name, request.content,
             content_length, requester.user
         )
 
diff --git a/synapse/server.py b/synapse/server.py
index a38e5179e0..10e3e9a4f1 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -31,6 +31,7 @@ from synapse.appservice.api import ApplicationServiceApi
 from synapse.appservice.scheduler import ApplicationServiceScheduler
 from synapse.crypto.keyring import Keyring
 from synapse.events.builder import EventBuilderFactory
+from synapse.events.spamcheck import SpamChecker
 from synapse.federation import initialize_http_replication
 from synapse.federation.send_queue import FederationRemoteSendQueue
 from synapse.federation.transport.client import TransportLayerClient
@@ -50,6 +51,10 @@ from synapse.handlers.initial_sync import InitialSyncHandler
 from synapse.handlers.receipts import ReceiptsHandler
 from synapse.handlers.read_marker import ReadMarkerHandler
 from synapse.handlers.user_directory import UserDirectoyHandler
+from synapse.handlers.groups_local import GroupsLocalHandler
+from synapse.handlers.profile import ProfileHandler
+from synapse.groups.groups_server import GroupsServerHandler
+from synapse.groups.attestations import GroupAttestionRenewer, GroupAttestationSigning
 from synapse.http.client import SimpleHttpClient, InsecureInterceptableContextFactory
 from synapse.http.matrixfederationclient import MatrixFederationHttpClient
 from synapse.notifier import Notifier
@@ -111,6 +116,7 @@ class HomeServer(object):
         'application_service_scheduler',
         'application_service_handler',
         'device_message_handler',
+        'profile_handler',
         'notifier',
         'distributor',
         'client_resource',
@@ -139,6 +145,11 @@ class HomeServer(object):
         'read_marker_handler',
         'action_generator',
         'user_directory_handler',
+        'groups_local_handler',
+        'groups_server_handler',
+        'groups_attestation_signing',
+        'groups_attestation_renewer',
+        'spam_checker',
     ]
 
     def __init__(self, hostname, **kwargs):
@@ -251,6 +262,9 @@ class HomeServer(object):
     def build_initial_sync_handler(self):
         return InitialSyncHandler(self)
 
+    def build_profile_handler(self):
+        return ProfileHandler(self)
+
     def build_event_sources(self):
         return EventSources(self)
 
@@ -309,6 +323,21 @@ class HomeServer(object):
     def build_user_directory_handler(self):
         return UserDirectoyHandler(self)
 
+    def build_groups_local_handler(self):
+        return GroupsLocalHandler(self)
+
+    def build_groups_server_handler(self):
+        return GroupsServerHandler(self)
+
+    def build_groups_attestation_signing(self):
+        return GroupAttestationSigning(self)
+
+    def build_groups_attestation_renewer(self):
+        return GroupAttestionRenewer(self)
+
+    def build_spam_checker(self):
+        return SpamChecker(self)
+
     def remove_pusher(self, app_id, push_key, user_id):
         return self.get_pusherpool().remove_pusher(app_id, push_key, user_id)
 
diff --git a/synapse/server.pyi b/synapse/server.pyi
index 9570df5537..e8c0386b7f 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -1,4 +1,6 @@
 import synapse.api.auth
+import synapse.federation.transaction_queue
+import synapse.federation.transport.client
 import synapse.handlers
 import synapse.handlers.auth
 import synapse.handlers.device
@@ -27,3 +29,9 @@ class HomeServer(object):
 
     def get_state_handler(self) -> synapse.state.StateHandler:
         pass
+
+    def get_federation_sender(self) -> synapse.federation.transaction_queue.TransactionQueue:
+        pass
+
+    def get_federation_transport_client(self) -> synapse.federation.transport.client.TransportLayerClient:
+        pass
diff --git a/synapse/state.py b/synapse/state.py
index 390799fbd5..dcdcdef65e 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -288,6 +288,9 @@ class StateHandler(object):
         """
         logger.debug("resolve_state_groups event_ids %s", event_ids)
 
+        # map from state group id to the state in that state group (where
+        # 'state' is a map from state key to event id)
+        # dict[int, dict[(str, str), str]]
         state_groups_ids = yield self.store.get_state_groups_ids(
             room_id, event_ids
         )
@@ -320,11 +323,15 @@ class StateHandler(object):
                 "Resolving state for %s with %d groups", room_id, len(state_groups_ids)
             )
 
+            # build a map from state key to the event_ids which set that state.
+            # dict[(str, str), set[str])
             state = {}
             for st in state_groups_ids.values():
                 for key, e_id in st.items():
                     state.setdefault(key, set()).add(e_id)
 
+            # build a map from state key to the event_ids which set that state,
+            # including only those where there are state keys in conflict.
             conflicted_state = {
                 k: list(v)
                 for k, v in state.items()
@@ -494,8 +501,14 @@ def _resolve_with_state_fac(unconflicted_state, conflicted_state,
 
     logger.info("Asking for %d conflicted events", len(needed_events))
 
+    # dict[str, FrozenEvent]: a map from state event id to event. Only includes
+    # the state events which are in conflict.
     state_map = yield state_map_factory(needed_events)
 
+    # get the ids of the auth events which allow us to authenticate the
+    # conflicted state, picking only from the unconflicting state.
+    #
+    # dict[(str, str), str]: a map from state key to event id
     auth_events = _create_auth_events_from_maps(
         unconflicted_state, conflicted_state, state_map
     )
diff --git a/synapse/storage/__init__.py b/synapse/storage/__init__.py
index b92472df33..594566eb38 100644
--- a/synapse/storage/__init__.py
+++ b/synapse/storage/__init__.py
@@ -37,7 +37,7 @@ from .media_repository import MediaRepositoryStore
 from .rejections import RejectionsStore
 from .event_push_actions import EventPushActionsStore
 from .deviceinbox import DeviceInboxStore
-
+from .group_server import GroupServerStore
 from .state import StateStore
 from .signatures import SignatureStore
 from .filtering import FilteringStore
@@ -88,6 +88,7 @@ class DataStore(RoomMemberStore, RoomStore,
                 DeviceStore,
                 DeviceInboxStore,
                 UserDirectoryStore,
+                GroupServerStore,
                 ):
 
     def __init__(self, db_conn, hs):
@@ -135,6 +136,9 @@ class DataStore(RoomMemberStore, RoomStore,
             db_conn, "pushers", "id",
             extra_tables=[("deleted_pushers", "stream_id")],
         )
+        self._group_updates_id_gen = StreamIdGenerator(
+            db_conn, "local_group_updates", "stream_id",
+        )
 
         if isinstance(self.database_engine, PostgresEngine):
             self._cache_id_gen = StreamIdGenerator(
@@ -235,6 +239,18 @@ class DataStore(RoomMemberStore, RoomStore,
             prefilled_cache=curr_state_delta_prefill,
         )
 
+        _group_updates_prefill, min_group_updates_id = self._get_cache_dict(
+            db_conn, "local_group_updates",
+            entity_column="user_id",
+            stream_column="stream_id",
+            max_value=self._group_updates_id_gen.get_current_token(),
+            limit=1000,
+        )
+        self._group_updates_stream_cache = StreamChangeCache(
+            "_group_updates_stream_cache", min_group_updates_id,
+            prefilled_cache=_group_updates_prefill,
+        )
+
         cur = LoggingTransaction(
             db_conn.cursor(),
             name="_find_stream_orderings_for_times_txn",
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 6f54036d67..5124a833a5 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -743,6 +743,33 @@ class SQLBaseStore(object):
         txn.execute(sql, values)
         return cls.cursor_to_dict(txn)
 
+    def _simple_update(self, table, keyvalues, updatevalues, desc):
+        return self.runInteraction(
+            desc,
+            self._simple_update_txn,
+            table, keyvalues, updatevalues,
+        )
+
+    @staticmethod
+    def _simple_update_txn(txn, table, keyvalues, updatevalues):
+        if keyvalues:
+            where = "WHERE %s" % " AND ".join("%s = ?" % k for k in keyvalues.iterkeys())
+        else:
+            where = ""
+
+        update_sql = "UPDATE %s SET %s %s" % (
+            table,
+            ", ".join("%s = ?" % (k,) for k in updatevalues),
+            where,
+        )
+
+        txn.execute(
+            update_sql,
+            updatevalues.values() + keyvalues.values()
+        )
+
+        return txn.rowcount
+
     def _simple_update_one(self, table, keyvalues, updatevalues,
                            desc="_simple_update_one"):
         """Executes an UPDATE query on the named table, setting new values for
@@ -768,27 +795,13 @@ class SQLBaseStore(object):
             table, keyvalues, updatevalues,
         )
 
-    @staticmethod
-    def _simple_update_one_txn(txn, table, keyvalues, updatevalues):
-        if keyvalues:
-            where = "WHERE %s" % " AND ".join("%s = ?" % k for k in keyvalues.iterkeys())
-        else:
-            where = ""
-
-        update_sql = "UPDATE %s SET %s %s" % (
-            table,
-            ", ".join("%s = ?" % (k,) for k in updatevalues),
-            where,
-        )
-
-        txn.execute(
-            update_sql,
-            updatevalues.values() + keyvalues.values()
-        )
+    @classmethod
+    def _simple_update_one_txn(cls, txn, table, keyvalues, updatevalues):
+        rowcount = cls._simple_update_txn(txn, table, keyvalues, updatevalues)
 
-        if txn.rowcount == 0:
+        if rowcount == 0:
             raise StoreError(404, "No row found")
-        if txn.rowcount > 1:
+        if rowcount > 1:
             raise StoreError(500, "More than one row matched")
 
     @staticmethod
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 7002b3752e..637640ec2a 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -21,7 +21,7 @@ from synapse.events.utils import prune_event
 
 from synapse.util.async import ObservableDeferred
 from synapse.util.logcontext import (
-    preserve_fn, PreserveLoggingContext, preserve_context_over_deferred
+    preserve_fn, PreserveLoggingContext, make_deferred_yieldable
 )
 from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
@@ -88,13 +88,23 @@ class _EventPeristenceQueue(object):
     def add_to_queue(self, room_id, events_and_contexts, backfilled):
         """Add events to the queue, with the given persist_event options.
 
+        NB: due to the normal usage pattern of this method, it does *not*
+        follow the synapse logcontext rules, and leaves the logcontext in
+        place whether or not the returned deferred is ready.
+
         Args:
             room_id (str):
             events_and_contexts (list[(EventBase, EventContext)]):
             backfilled (bool):
+
+        Returns:
+            defer.Deferred: a deferred which will resolve once the events are
+                persisted. Runs its callbacks *without* a logcontext.
         """
         queue = self._event_persist_queues.setdefault(room_id, deque())
         if queue:
+            # if the last item in the queue has the same `backfilled` setting,
+            # we can just add these new events to that item.
             end_item = queue[-1]
             if end_item.backfilled == backfilled:
                 end_item.events_and_contexts.extend(events_and_contexts)
@@ -113,11 +123,11 @@ class _EventPeristenceQueue(object):
     def handle_queue(self, room_id, per_item_callback):
         """Attempts to handle the queue for a room if not already being handled.
 
-        The given callback will be invoked with for each item in the queue,1
+        The given callback will be invoked with for each item in the queue,
         of type _EventPersistQueueItem. The per_item_callback will continuously
         be called with new items, unless the queue becomnes empty. The return
         value of the function will be given to the deferreds waiting on the item,
-        exceptions will be passed to the deferres as well.
+        exceptions will be passed to the deferreds as well.
 
         This function should therefore be called whenever anything is added
         to the queue.
@@ -233,7 +243,7 @@ class EventsStore(SQLBaseStore):
 
         deferreds = []
         for room_id, evs_ctxs in partitioned.iteritems():
-            d = preserve_fn(self._event_persist_queue.add_to_queue)(
+            d = self._event_persist_queue.add_to_queue(
                 room_id, evs_ctxs,
                 backfilled=backfilled,
             )
@@ -242,7 +252,7 @@ class EventsStore(SQLBaseStore):
         for room_id in partitioned:
             self._maybe_start_persisting(room_id)
 
-        return preserve_context_over_deferred(
+        return make_deferred_yieldable(
             defer.gatherResults(deferreds, consumeErrors=True)
         )
 
@@ -267,7 +277,7 @@ class EventsStore(SQLBaseStore):
 
         self._maybe_start_persisting(event.room_id)
 
-        yield preserve_context_over_deferred(deferred)
+        yield make_deferred_yieldable(deferred)
 
         max_persisted_id = yield self._stream_id_gen.get_current_token()
         defer.returnValue((event.internal_metadata.stream_ordering, max_persisted_id))
@@ -784,6 +794,9 @@ class EventsStore(SQLBaseStore):
                     self._invalidate_cache_and_stream(
                         txn, self.is_host_joined, (room_id, host)
                     )
+                    self._invalidate_cache_and_stream(
+                        txn, self.was_host_joined, (room_id, host)
+                    )
 
                 self._invalidate_cache_and_stream(
                     txn, self.get_users_in_room, (room_id,)
@@ -1523,7 +1536,7 @@ class EventsStore(SQLBaseStore):
         if not allow_rejected:
             rows[:] = [r for r in rows if not r["rejects"]]
 
-        res = yield preserve_context_over_deferred(defer.gatherResults(
+        res = yield make_deferred_yieldable(defer.gatherResults(
             [
                 preserve_fn(self._get_event_from_row)(
                     row["internal_metadata"], row["json"], row["redacts"],
diff --git a/synapse/storage/group_server.py b/synapse/storage/group_server.py
new file mode 100644
index 0000000000..9e63db5c6c
--- /dev/null
+++ b/synapse/storage/group_server.py
@@ -0,0 +1,1199 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from twisted.internet import defer
+
+from synapse.api.errors import SynapseError
+
+from ._base import SQLBaseStore
+
+import ujson as json
+
+
+# The category ID for the "default" category. We don't store as null in the
+# database to avoid the fun of null != null
+_DEFAULT_CATEGORY_ID = ""
+_DEFAULT_ROLE_ID = ""
+
+
+class GroupServerStore(SQLBaseStore):
+    def get_group(self, group_id):
+        return self._simple_select_one(
+            table="groups",
+            keyvalues={
+                "group_id": group_id,
+            },
+            retcols=("name", "short_description", "long_description", "avatar_url",),
+            allow_none=True,
+            desc="is_user_in_group",
+        )
+
+    def get_users_in_group(self, group_id, include_private=False):
+        # TODO: Pagination
+
+        keyvalues = {
+            "group_id": group_id,
+        }
+        if not include_private:
+            keyvalues["is_public"] = True
+
+        return self._simple_select_list(
+            table="group_users",
+            keyvalues=keyvalues,
+            retcols=("user_id", "is_public",),
+            desc="get_users_in_group",
+        )
+
+    def get_invited_users_in_group(self, group_id):
+        # TODO: Pagination
+
+        return self._simple_select_onecol(
+            table="group_invites",
+            keyvalues={
+                "group_id": group_id,
+            },
+            retcol="user_id",
+            desc="get_invited_users_in_group",
+        )
+
+    def get_rooms_in_group(self, group_id, include_private=False):
+        # TODO: Pagination
+
+        keyvalues = {
+            "group_id": group_id,
+        }
+        if not include_private:
+            keyvalues["is_public"] = True
+
+        return self._simple_select_list(
+            table="group_rooms",
+            keyvalues=keyvalues,
+            retcols=("room_id", "is_public",),
+            desc="get_rooms_in_group",
+        )
+
+    def get_rooms_for_summary_by_category(self, group_id, include_private=False):
+        """Get the rooms and categories that should be included in a summary request
+
+        Returns ([rooms], [categories])
+        """
+        def _get_rooms_for_summary_txn(txn):
+            keyvalues = {
+                "group_id": group_id,
+            }
+            if not include_private:
+                keyvalues["is_public"] = True
+
+            sql = """
+                SELECT room_id, is_public, category_id, room_order
+                FROM group_summary_rooms
+                WHERE group_id = ?
+            """
+
+            if not include_private:
+                sql += " AND is_public = ?"
+                txn.execute(sql, (group_id, True))
+            else:
+                txn.execute(sql, (group_id,))
+
+            rooms = [
+                {
+                    "room_id": row[0],
+                    "is_public": row[1],
+                    "category_id": row[2] if row[2] != _DEFAULT_CATEGORY_ID else None,
+                    "order": row[3],
+                }
+                for row in txn
+            ]
+
+            sql = """
+                SELECT category_id, is_public, profile, cat_order
+                FROM group_summary_room_categories
+                INNER JOIN group_room_categories USING (group_id, category_id)
+                WHERE group_id = ?
+            """
+
+            if not include_private:
+                sql += " AND is_public = ?"
+                txn.execute(sql, (group_id, True))
+            else:
+                txn.execute(sql, (group_id,))
+
+            categories = {
+                row[0]: {
+                    "is_public": row[1],
+                    "profile": json.loads(row[2]),
+                    "order": row[3],
+                }
+                for row in txn
+            }
+
+            return rooms, categories
+        return self.runInteraction(
+            "get_rooms_for_summary", _get_rooms_for_summary_txn
+        )
+
+    def add_room_to_summary(self, group_id, room_id, category_id, order, is_public):
+        return self.runInteraction(
+            "add_room_to_summary", self._add_room_to_summary_txn,
+            group_id, room_id, category_id, order, is_public,
+        )
+
+    def _add_room_to_summary_txn(self, txn, group_id, room_id, category_id, order,
+                                 is_public):
+        """Add (or update) room's entry in summary.
+
+        Args:
+            group_id (str)
+            room_id (str)
+            category_id (str): If not None then adds the category to the end of
+                the summary if its not already there. [Optional]
+            order (int): If not None inserts the room at that position, e.g.
+                an order of 1 will put the room first. Otherwise, the room gets
+                added to the end.
+        """
+        room_in_group = self._simple_select_one_onecol_txn(
+            txn,
+            table="group_rooms",
+            keyvalues={
+                "group_id": group_id,
+                "room_id": room_id,
+            },
+            retcol="room_id",
+            allow_none=True,
+        )
+        if not room_in_group:
+            raise SynapseError(400, "room not in group")
+
+        if category_id is None:
+            category_id = _DEFAULT_CATEGORY_ID
+        else:
+            cat_exists = self._simple_select_one_onecol_txn(
+                txn,
+                table="group_room_categories",
+                keyvalues={
+                    "group_id": group_id,
+                    "category_id": category_id,
+                },
+                retcol="group_id",
+                allow_none=True,
+            )
+            if not cat_exists:
+                raise SynapseError(400, "Category doesn't exist")
+
+            # TODO: Check category is part of summary already
+            cat_exists = self._simple_select_one_onecol_txn(
+                txn,
+                table="group_summary_room_categories",
+                keyvalues={
+                    "group_id": group_id,
+                    "category_id": category_id,
+                },
+                retcol="group_id",
+                allow_none=True,
+            )
+            if not cat_exists:
+                # If not, add it with an order larger than all others
+                txn.execute("""
+                    INSERT INTO group_summary_room_categories
+                    (group_id, category_id, cat_order)
+                    SELECT ?, ?, COALESCE(MAX(cat_order), 0) + 1
+                    FROM group_summary_room_categories
+                    WHERE group_id = ? AND category_id = ?
+                """, (group_id, category_id, group_id, category_id))
+
+        existing = self._simple_select_one_txn(
+            txn,
+            table="group_summary_rooms",
+            keyvalues={
+                "group_id": group_id,
+                "room_id": room_id,
+                "category_id": category_id,
+            },
+            retcols=("room_order", "is_public",),
+            allow_none=True,
+        )
+
+        if order is not None:
+            # Shuffle other room orders that come after the given order
+            sql = """
+                UPDATE group_summary_rooms SET room_order = room_order + 1
+                WHERE group_id = ? AND category_id = ? AND room_order >= ?
+            """
+            txn.execute(sql, (group_id, category_id, order,))
+        elif not existing:
+            sql = """
+                SELECT COALESCE(MAX(room_order), 0) + 1 FROM group_summary_rooms
+                WHERE group_id = ? AND category_id = ?
+            """
+            txn.execute(sql, (group_id, category_id,))
+            order, = txn.fetchone()
+
+        if existing:
+            to_update = {}
+            if order is not None:
+                to_update["room_order"] = order
+            if is_public is not None:
+                to_update["is_public"] = is_public
+            self._simple_update_txn(
+                txn,
+                table="group_summary_rooms",
+                keyvalues={
+                    "group_id": group_id,
+                    "category_id": category_id,
+                    "room_id": room_id,
+                },
+                values=to_update,
+            )
+        else:
+            if is_public is None:
+                is_public = True
+
+            self._simple_insert_txn(
+                txn,
+                table="group_summary_rooms",
+                values={
+                    "group_id": group_id,
+                    "category_id": category_id,
+                    "room_id": room_id,
+                    "room_order": order,
+                    "is_public": is_public,
+                },
+            )
+
+    def remove_room_from_summary(self, group_id, room_id, category_id):
+        if category_id is None:
+            category_id = _DEFAULT_CATEGORY_ID
+
+        return self._simple_delete(
+            table="group_summary_rooms",
+            keyvalues={
+                "group_id": group_id,
+                "category_id": category_id,
+                "room_id": room_id,
+            },
+            desc="remove_room_from_summary",
+        )
+
+    @defer.inlineCallbacks
+    def get_group_categories(self, group_id):
+        rows = yield self._simple_select_list(
+            table="group_room_categories",
+            keyvalues={
+                "group_id": group_id,
+            },
+            retcols=("category_id", "is_public", "profile"),
+            desc="get_group_categories",
+        )
+
+        defer.returnValue({
+            row["category_id"]: {
+                "is_public": row["is_public"],
+                "profile": json.loads(row["profile"]),
+            }
+            for row in rows
+        })
+
+    @defer.inlineCallbacks
+    def get_group_category(self, group_id, category_id):
+        category = yield self._simple_select_one(
+            table="group_room_categories",
+            keyvalues={
+                "group_id": group_id,
+                "category_id": category_id,
+            },
+            retcols=("is_public", "profile"),
+            desc="get_group_category",
+        )
+
+        category["profile"] = json.loads(category["profile"])
+
+        defer.returnValue(category)
+
+    def upsert_group_category(self, group_id, category_id, profile, is_public):
+        """Add/update room category for group
+        """
+        insertion_values = {}
+        update_values = {"category_id": category_id}  # This cannot be empty
+
+        if profile is None:
+            insertion_values["profile"] = "{}"
+        else:
+            update_values["profile"] = json.dumps(profile)
+
+        if is_public is None:
+            insertion_values["is_public"] = True
+        else:
+            update_values["is_public"] = is_public
+
+        return self._simple_upsert(
+            table="group_room_categories",
+            keyvalues={
+                "group_id": group_id,
+                "category_id": category_id,
+            },
+            values=update_values,
+            insertion_values=insertion_values,
+            desc="upsert_group_category",
+        )
+
+    def remove_group_category(self, group_id, category_id):
+        return self._simple_delete(
+            table="group_room_categories",
+            keyvalues={
+                "group_id": group_id,
+                "category_id": category_id,
+            },
+            desc="remove_group_category",
+        )
+
+    @defer.inlineCallbacks
+    def get_group_roles(self, group_id):
+        rows = yield self._simple_select_list(
+            table="group_roles",
+            keyvalues={
+                "group_id": group_id,
+            },
+            retcols=("role_id", "is_public", "profile"),
+            desc="get_group_roles",
+        )
+
+        defer.returnValue({
+            row["role_id"]: {
+                "is_public": row["is_public"],
+                "profile": json.loads(row["profile"]),
+            }
+            for row in rows
+        })
+
+    @defer.inlineCallbacks
+    def get_group_role(self, group_id, role_id):
+        role = yield self._simple_select_one(
+            table="group_roles",
+            keyvalues={
+                "group_id": group_id,
+                "role_id": role_id,
+            },
+            retcols=("is_public", "profile"),
+            desc="get_group_role",
+        )
+
+        role["profile"] = json.loads(role["profile"])
+
+        defer.returnValue(role)
+
+    def upsert_group_role(self, group_id, role_id, profile, is_public):
+        """Add/remove user role
+        """
+        insertion_values = {}
+        update_values = {"role_id": role_id}  # This cannot be empty
+
+        if profile is None:
+            insertion_values["profile"] = "{}"
+        else:
+            update_values["profile"] = json.dumps(profile)
+
+        if is_public is None:
+            insertion_values["is_public"] = True
+        else:
+            update_values["is_public"] = is_public
+
+        return self._simple_upsert(
+            table="group_roles",
+            keyvalues={
+                "group_id": group_id,
+                "role_id": role_id,
+            },
+            values=update_values,
+            insertion_values=insertion_values,
+            desc="upsert_group_role",
+        )
+
+    def remove_group_role(self, group_id, role_id):
+        return self._simple_delete(
+            table="group_roles",
+            keyvalues={
+                "group_id": group_id,
+                "role_id": role_id,
+            },
+            desc="remove_group_role",
+        )
+
+    def add_user_to_summary(self, group_id, user_id, role_id, order, is_public):
+        return self.runInteraction(
+            "add_user_to_summary", self._add_user_to_summary_txn,
+            group_id, user_id, role_id, order, is_public,
+        )
+
+    def _add_user_to_summary_txn(self, txn, group_id, user_id, role_id, order,
+                                 is_public):
+        """Add (or update) user's entry in summary.
+
+        Args:
+            group_id (str)
+            user_id (str)
+            role_id (str): If not None then adds the role to the end of
+                the summary if its not already there. [Optional]
+            order (int): If not None inserts the user at that position, e.g.
+                an order of 1 will put the user first. Otherwise, the user gets
+                added to the end.
+        """
+        user_in_group = self._simple_select_one_onecol_txn(
+            txn,
+            table="group_users",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            retcol="user_id",
+            allow_none=True,
+        )
+        if not user_in_group:
+            raise SynapseError(400, "user not in group")
+
+        if role_id is None:
+            role_id = _DEFAULT_ROLE_ID
+        else:
+            role_exists = self._simple_select_one_onecol_txn(
+                txn,
+                table="group_roles",
+                keyvalues={
+                    "group_id": group_id,
+                    "role_id": role_id,
+                },
+                retcol="group_id",
+                allow_none=True,
+            )
+            if not role_exists:
+                raise SynapseError(400, "Role doesn't exist")
+
+            # TODO: Check role is part of the summary already
+            role_exists = self._simple_select_one_onecol_txn(
+                txn,
+                table="group_summary_roles",
+                keyvalues={
+                    "group_id": group_id,
+                    "role_id": role_id,
+                },
+                retcol="group_id",
+                allow_none=True,
+            )
+            if not role_exists:
+                # If not, add it with an order larger than all others
+                txn.execute("""
+                    INSERT INTO group_summary_roles
+                    (group_id, role_id, role_order)
+                    SELECT ?, ?, COALESCE(MAX(role_order), 0) + 1
+                    FROM group_summary_roles
+                    WHERE group_id = ? AND role_id = ?
+                """, (group_id, role_id, group_id, role_id))
+
+        existing = self._simple_select_one_txn(
+            txn,
+            table="group_summary_users",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+                "role_id": role_id,
+            },
+            retcols=("user_order", "is_public",),
+            allow_none=True,
+        )
+
+        if order is not None:
+            # Shuffle other users orders that come after the given order
+            sql = """
+                UPDATE group_summary_users SET user_order = user_order + 1
+                WHERE group_id = ? AND role_id = ? AND user_order >= ?
+            """
+            txn.execute(sql, (group_id, role_id, order,))
+        elif not existing:
+            sql = """
+                SELECT COALESCE(MAX(user_order), 0) + 1 FROM group_summary_users
+                WHERE group_id = ? AND role_id = ?
+            """
+            txn.execute(sql, (group_id, role_id,))
+            order, = txn.fetchone()
+
+        if existing:
+            to_update = {}
+            if order is not None:
+                to_update["user_order"] = order
+            if is_public is not None:
+                to_update["is_public"] = is_public
+            self._simple_update_txn(
+                txn,
+                table="group_summary_users",
+                keyvalues={
+                    "group_id": group_id,
+                    "role_id": role_id,
+                    "user_id": user_id,
+                },
+                values=to_update,
+            )
+        else:
+            if is_public is None:
+                is_public = True
+
+            self._simple_insert_txn(
+                txn,
+                table="group_summary_users",
+                values={
+                    "group_id": group_id,
+                    "role_id": role_id,
+                    "user_id": user_id,
+                    "user_order": order,
+                    "is_public": is_public,
+                },
+            )
+
+    def remove_user_from_summary(self, group_id, user_id, role_id):
+        if role_id is None:
+            role_id = _DEFAULT_ROLE_ID
+
+        return self._simple_delete(
+            table="group_summary_users",
+            keyvalues={
+                "group_id": group_id,
+                "role_id": role_id,
+                "user_id": user_id,
+            },
+            desc="remove_user_from_summary",
+        )
+
+    def get_users_for_summary_by_role(self, group_id, include_private=False):
+        """Get the users and roles that should be included in a summary request
+
+        Returns ([users], [roles])
+        """
+        def _get_users_for_summary_txn(txn):
+            keyvalues = {
+                "group_id": group_id,
+            }
+            if not include_private:
+                keyvalues["is_public"] = True
+
+            sql = """
+                SELECT user_id, is_public, role_id, user_order
+                FROM group_summary_users
+                WHERE group_id = ?
+            """
+
+            if not include_private:
+                sql += " AND is_public = ?"
+                txn.execute(sql, (group_id, True))
+            else:
+                txn.execute(sql, (group_id,))
+
+            users = [
+                {
+                    "user_id": row[0],
+                    "is_public": row[1],
+                    "role_id": row[2] if row[2] != _DEFAULT_ROLE_ID else None,
+                    "order": row[3],
+                }
+                for row in txn
+            ]
+
+            sql = """
+                SELECT role_id, is_public, profile, role_order
+                FROM group_summary_roles
+                INNER JOIN group_roles USING (group_id, role_id)
+                WHERE group_id = ?
+            """
+
+            if not include_private:
+                sql += " AND is_public = ?"
+                txn.execute(sql, (group_id, True))
+            else:
+                txn.execute(sql, (group_id,))
+
+            roles = {
+                row[0]: {
+                    "is_public": row[1],
+                    "profile": json.loads(row[2]),
+                    "order": row[3],
+                }
+                for row in txn
+            }
+
+            return users, roles
+        return self.runInteraction(
+            "get_users_for_summary_by_role", _get_users_for_summary_txn
+        )
+
+    def is_user_in_group(self, user_id, group_id):
+        return self._simple_select_one_onecol(
+            table="group_users",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            retcol="user_id",
+            allow_none=True,
+            desc="is_user_in_group",
+        ).addCallback(lambda r: bool(r))
+
+    def is_user_admin_in_group(self, group_id, user_id):
+        return self._simple_select_one_onecol(
+            table="group_users",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            retcol="is_admin",
+            allow_none=True,
+            desc="is_user_admin_in_group",
+        )
+
+    def add_group_invite(self, group_id, user_id):
+        """Record that the group server has invited a user
+        """
+        return self._simple_insert(
+            table="group_invites",
+            values={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            desc="add_group_invite",
+        )
+
+    def is_user_invited_to_local_group(self, group_id, user_id):
+        """Has the group server invited a user?
+        """
+        return self._simple_select_one_onecol(
+            table="group_invites",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            retcol="user_id",
+            desc="is_user_invited_to_local_group",
+            allow_none=True,
+        )
+
+    def get_users_membership_info_in_group(self, group_id, user_id):
+        """Get a dict describing the membership of a user in a group.
+
+        Example if joined:
+
+            {
+                "membership": "join",
+                "is_public": True,
+                "is_privileged": False,
+            }
+
+        Returns an empty dict if the user is not join/invite/etc
+        """
+        def _get_users_membership_in_group_txn(txn):
+            row = self._simple_select_one_txn(
+                txn,
+                table="group_users",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+                retcols=("is_admin", "is_public"),
+                allow_none=True,
+            )
+
+            if row:
+                return {
+                    "membership": "join",
+                    "is_public": row["is_public"],
+                    "is_privileged": row["is_admin"],
+                }
+
+            row = self._simple_select_one_onecol_txn(
+                txn,
+                table="group_invites",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+                retcol="user_id",
+                allow_none=True,
+            )
+
+            if row:
+                return {
+                    "membership": "invite",
+                }
+
+            return {}
+
+        return self.runInteraction(
+            "get_users_membership_info_in_group", _get_users_membership_in_group_txn,
+        )
+
+    def add_user_to_group(self, group_id, user_id, is_admin=False, is_public=True,
+                          local_attestation=None, remote_attestation=None):
+        """Add a user to the group server.
+
+        Args:
+            group_id (str)
+            user_id (str)
+            is_admin (bool)
+            is_public (bool)
+            local_attestation (dict): The attestation the GS created to give
+                to the remote server. Optional if the user and group are on the
+                same server
+            remote_attestation (dict): The attestation given to GS by remote
+                server. Optional if the user and group are on the same server
+        """
+        def _add_user_to_group_txn(txn):
+            self._simple_insert_txn(
+                txn,
+                table="group_users",
+                values={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                    "is_admin": is_admin,
+                    "is_public": is_public,
+                },
+            )
+
+            self._simple_delete_txn(
+                txn,
+                table="group_invites",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+
+            if local_attestation:
+                self._simple_insert_txn(
+                    txn,
+                    table="group_attestations_renewals",
+                    values={
+                        "group_id": group_id,
+                        "user_id": user_id,
+                        "valid_until_ms": local_attestation["valid_until_ms"],
+                    },
+                )
+            if remote_attestation:
+                self._simple_insert_txn(
+                    txn,
+                    table="group_attestations_remote",
+                    values={
+                        "group_id": group_id,
+                        "user_id": user_id,
+                        "valid_until_ms": remote_attestation["valid_until_ms"],
+                        "attestation_json": json.dumps(remote_attestation),
+                    },
+                )
+
+        return self.runInteraction(
+            "add_user_to_group", _add_user_to_group_txn
+        )
+
+    def remove_user_from_group(self, group_id, user_id):
+        def _remove_user_from_group_txn(txn):
+            self._simple_delete_txn(
+                txn,
+                table="group_users",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+            self._simple_delete_txn(
+                txn,
+                table="group_invites",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+            self._simple_delete_txn(
+                txn,
+                table="group_attestations_renewals",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+            self._simple_delete_txn(
+                txn,
+                table="group_attestations_remote",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+            self._simple_delete_txn(
+                txn,
+                table="group_summary_users",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+        return self.runInteraction("remove_user_from_group", _remove_user_from_group_txn)
+
+    def add_room_to_group(self, group_id, room_id, is_public):
+        return self._simple_insert(
+            table="group_rooms",
+            values={
+                "group_id": group_id,
+                "room_id": room_id,
+                "is_public": is_public,
+            },
+            desc="add_room_to_group",
+        )
+
+    def remove_room_from_group(self, group_id, room_id):
+        def _remove_room_from_group_txn(txn):
+            self._simple_delete_txn(
+                txn,
+                table="group_rooms",
+                keyvalues={
+                    "group_id": group_id,
+                    "room_id": room_id,
+                },
+            )
+
+            self._simple_delete_txn(
+                txn,
+                table="group_summary_rooms",
+                keyvalues={
+                    "group_id": group_id,
+                    "room_id": room_id,
+                },
+            )
+        return self.runInteraction(
+            "remove_room_from_group", _remove_room_from_group_txn,
+        )
+
+    def get_publicised_groups_for_user(self, user_id):
+        """Get all groups a user is publicising
+        """
+        return self._simple_select_onecol(
+            table="local_group_membership",
+            keyvalues={
+                "user_id": user_id,
+                "membership": "join",
+                "is_publicised": True,
+            },
+            retcol="group_id",
+            desc="get_publicised_groups_for_user",
+        )
+
+    def update_group_publicity(self, group_id, user_id, publicise):
+        """Update whether the user is publicising their membership of the group
+        """
+        return self._simple_update_one(
+            table="local_group_membership",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            updatevalues={
+                "is_publicised": publicise,
+            },
+            desc="update_group_publicity"
+        )
+
+    @defer.inlineCallbacks
+    def register_user_group_membership(self, group_id, user_id, membership,
+                                       is_admin=False, content={},
+                                       local_attestation=None,
+                                       remote_attestation=None,
+                                       is_publicised=False,
+                                       ):
+        """Registers that a local user is a member of a (local or remote) group.
+
+        Args:
+            group_id (str)
+            user_id (str)
+            membership (str)
+            is_admin (bool)
+            content (dict): Content of the membership, e.g. includes the inviter
+                if the user has been invited.
+            local_attestation (dict): If remote group then store the fact that we
+                have given out an attestation, else None.
+            remote_attestation (dict): If remote group then store the remote
+                attestation from the group, else None.
+        """
+        def _register_user_group_membership_txn(txn, next_id):
+            # TODO: Upsert?
+            self._simple_delete_txn(
+                txn,
+                table="local_group_membership",
+                keyvalues={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                },
+            )
+            self._simple_insert_txn(
+                txn,
+                table="local_group_membership",
+                values={
+                    "group_id": group_id,
+                    "user_id": user_id,
+                    "is_admin": is_admin,
+                    "membership": membership,
+                    "is_publicised": is_publicised,
+                    "content": json.dumps(content),
+                },
+            )
+
+            self._simple_insert_txn(
+                txn,
+                table="local_group_updates",
+                values={
+                    "stream_id": next_id,
+                    "group_id": group_id,
+                    "user_id": user_id,
+                    "type": "membership",
+                    "content": json.dumps({"membership": membership, "content": content}),
+                }
+            )
+            self._group_updates_stream_cache.entity_has_changed(user_id, next_id)
+
+            # TODO: Insert profile to ensure it comes down stream if its a join.
+
+            if membership == "join":
+                if local_attestation:
+                    self._simple_insert_txn(
+                        txn,
+                        table="group_attestations_renewals",
+                        values={
+                            "group_id": group_id,
+                            "user_id": user_id,
+                            "valid_until_ms": local_attestation["valid_until_ms"],
+                        }
+                    )
+                if remote_attestation:
+                    self._simple_insert_txn(
+                        txn,
+                        table="group_attestations_remote",
+                        values={
+                            "group_id": group_id,
+                            "user_id": user_id,
+                            "valid_until_ms": remote_attestation["valid_until_ms"],
+                            "attestation_json": json.dumps(remote_attestation),
+                        }
+                    )
+            else:
+                self._simple_delete_txn(
+                    txn,
+                    table="group_attestations_renewals",
+                    keyvalues={
+                        "group_id": group_id,
+                        "user_id": user_id,
+                    },
+                )
+                self._simple_delete_txn(
+                    txn,
+                    table="group_attestations_remote",
+                    keyvalues={
+                        "group_id": group_id,
+                        "user_id": user_id,
+                    },
+                )
+
+            return next_id
+
+        with self._group_updates_id_gen.get_next() as next_id:
+            res = yield self.runInteraction(
+                "register_user_group_membership",
+                _register_user_group_membership_txn, next_id,
+            )
+        defer.returnValue(res)
+
+    @defer.inlineCallbacks
+    def create_group(self, group_id, user_id, name, avatar_url, short_description,
+                     long_description,):
+        yield self._simple_insert(
+            table="groups",
+            values={
+                "group_id": group_id,
+                "name": name,
+                "avatar_url": avatar_url,
+                "short_description": short_description,
+                "long_description": long_description,
+            },
+            desc="create_group",
+        )
+
+    @defer.inlineCallbacks
+    def update_group_profile(self, group_id, profile,):
+        yield self._simple_update_one(
+            table="groups",
+            keyvalues={
+                "group_id": group_id,
+            },
+            updatevalues=profile,
+            desc="update_group_profile",
+        )
+
+    def get_attestations_need_renewals(self, valid_until_ms):
+        """Get all attestations that need to be renewed until givent time
+        """
+        def _get_attestations_need_renewals_txn(txn):
+            sql = """
+                SELECT group_id, user_id FROM group_attestations_renewals
+                WHERE valid_until_ms <= ?
+            """
+            txn.execute(sql, (valid_until_ms,))
+            return self.cursor_to_dict(txn)
+        return self.runInteraction(
+            "get_attestations_need_renewals", _get_attestations_need_renewals_txn
+        )
+
+    def update_attestation_renewal(self, group_id, user_id, attestation):
+        """Update an attestation that we have renewed
+        """
+        return self._simple_update_one(
+            table="group_attestations_renewals",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            updatevalues={
+                "valid_until_ms": attestation["valid_until_ms"],
+            },
+            desc="update_attestation_renewal",
+        )
+
+    def update_remote_attestion(self, group_id, user_id, attestation):
+        """Update an attestation that a remote has renewed
+        """
+        return self._simple_update_one(
+            table="group_attestations_remote",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            updatevalues={
+                "valid_until_ms": attestation["valid_until_ms"],
+                "attestation_json": json.dumps(attestation)
+            },
+            desc="update_remote_attestion",
+        )
+
+    @defer.inlineCallbacks
+    def get_remote_attestation(self, group_id, user_id):
+        """Get the attestation that proves the remote agrees that the user is
+        in the group.
+        """
+        row = yield self._simple_select_one(
+            table="group_attestations_remote",
+            keyvalues={
+                "group_id": group_id,
+                "user_id": user_id,
+            },
+            retcols=("valid_until_ms", "attestation_json"),
+            desc="get_remote_attestation",
+            allow_none=True,
+        )
+
+        now = int(self._clock.time_msec())
+        if row and now < row["valid_until_ms"]:
+            defer.returnValue(json.loads(row["attestation_json"]))
+
+        defer.returnValue(None)
+
+    def get_joined_groups(self, user_id):
+        return self._simple_select_onecol(
+            table="local_group_membership",
+            keyvalues={
+                "user_id": user_id,
+                "membership": "join",
+            },
+            retcol="group_id",
+            desc="get_joined_groups",
+        )
+
+    def get_all_groups_for_user(self, user_id, now_token):
+        def _get_all_groups_for_user_txn(txn):
+            sql = """
+                SELECT group_id, type, membership, u.content
+                FROM local_group_updates AS u
+                INNER JOIN local_group_membership USING (group_id, user_id)
+                WHERE user_id = ? AND membership != 'leave'
+                    AND stream_id <= ?
+            """
+            txn.execute(sql, (user_id, now_token,))
+            return [
+                {
+                    "group_id": row[0],
+                    "type": row[1],
+                    "membership": row[2],
+                    "content": json.loads(row[3]),
+                }
+                for row in txn
+            ]
+        return self.runInteraction(
+            "get_all_groups_for_user", _get_all_groups_for_user_txn,
+        )
+
+    def get_groups_changes_for_user(self, user_id, from_token, to_token):
+        from_token = int(from_token)
+        has_changed = self._group_updates_stream_cache.has_entity_changed(
+            user_id, from_token,
+        )
+        if not has_changed:
+            return []
+
+        def _get_groups_changes_for_user_txn(txn):
+            sql = """
+                SELECT group_id, membership, type, u.content
+                FROM local_group_updates AS u
+                INNER JOIN local_group_membership USING (group_id, user_id)
+                WHERE user_id = ? AND ? < stream_id AND stream_id <= ?
+            """
+            txn.execute(sql, (user_id, from_token, to_token,))
+            return [{
+                "group_id": group_id,
+                "membership": membership,
+                "type": gtype,
+                "content": json.loads(content_json),
+            } for group_id, membership, gtype, content_json in txn]
+        return self.runInteraction(
+            "get_groups_changes_for_user", _get_groups_changes_for_user_txn,
+        )
+
+    def get_all_groups_changes(self, from_token, to_token, limit):
+        from_token = int(from_token)
+        has_changed = self._group_updates_stream_cache.has_any_entity_changed(
+            from_token,
+        )
+        if not has_changed:
+            return []
+
+        def _get_all_groups_changes_txn(txn):
+            sql = """
+                SELECT stream_id, group_id, user_id, type, content
+                FROM local_group_updates
+                WHERE ? < stream_id AND stream_id <= ?
+                LIMIT ?
+            """
+            txn.execute(sql, (from_token, to_token, limit,))
+            return [(
+                stream_id,
+                group_id,
+                user_id,
+                gtype,
+                json.loads(content_json),
+            ) for stream_id, group_id, user_id, gtype, content_json in txn]
+        return self.runInteraction(
+            "get_all_groups_changes", _get_all_groups_changes_txn,
+        )
+
+    def get_group_stream_token(self):
+        return self._group_updates_id_gen.get_current_token()
diff --git a/synapse/storage/media_repository.py b/synapse/storage/media_repository.py
index 82bb61b811..7110a71279 100644
--- a/synapse/storage/media_repository.py
+++ b/synapse/storage/media_repository.py
@@ -62,7 +62,7 @@ class MediaRepositoryStore(SQLBaseStore):
         def get_url_cache_txn(txn):
             # get the most recently cached result (relative to the given ts)
             sql = (
-                "SELECT response_code, etag, expires, og, media_id, download_ts"
+                "SELECT response_code, etag, expires_ts, og, media_id, download_ts"
                 " FROM local_media_repository_url_cache"
                 " WHERE url = ? AND download_ts <= ?"
                 " ORDER BY download_ts DESC LIMIT 1"
@@ -74,7 +74,7 @@ class MediaRepositoryStore(SQLBaseStore):
                 # ...or if we've requested a timestamp older than the oldest
                 # copy in the cache, return the oldest copy (if any)
                 sql = (
-                    "SELECT response_code, etag, expires, og, media_id, download_ts"
+                    "SELECT response_code, etag, expires_ts, og, media_id, download_ts"
                     " FROM local_media_repository_url_cache"
                     " WHERE url = ? AND download_ts > ?"
                     " ORDER BY download_ts ASC LIMIT 1"
@@ -86,14 +86,14 @@ class MediaRepositoryStore(SQLBaseStore):
                 return None
 
             return dict(zip((
-                'response_code', 'etag', 'expires', 'og', 'media_id', 'download_ts'
+                'response_code', 'etag', 'expires_ts', 'og', 'media_id', 'download_ts'
             ), row))
 
         return self.runInteraction(
             "get_url_cache", get_url_cache_txn
         )
 
-    def store_url_cache(self, url, response_code, etag, expires, og, media_id,
+    def store_url_cache(self, url, response_code, etag, expires_ts, og, media_id,
                         download_ts):
         return self._simple_insert(
             "local_media_repository_url_cache",
@@ -101,7 +101,7 @@ class MediaRepositoryStore(SQLBaseStore):
                 "url": url,
                 "response_code": response_code,
                 "etag": etag,
-                "expires": expires,
+                "expires_ts": expires_ts,
                 "og": og,
                 "media_id": media_id,
                 "download_ts": download_ts,
@@ -238,3 +238,64 @@ class MediaRepositoryStore(SQLBaseStore):
                 },
             )
         return self.runInteraction("delete_remote_media", delete_remote_media_txn)
+
+    def get_expired_url_cache(self, now_ts):
+        sql = (
+            "SELECT media_id FROM local_media_repository_url_cache"
+            " WHERE expires_ts < ?"
+            " ORDER BY expires_ts ASC"
+            " LIMIT 500"
+        )
+
+        def _get_expired_url_cache_txn(txn):
+            txn.execute(sql, (now_ts,))
+            return [row[0] for row in txn]
+
+        return self.runInteraction("get_expired_url_cache", _get_expired_url_cache_txn)
+
+    def delete_url_cache(self, media_ids):
+        sql = (
+            "DELETE FROM local_media_repository_url_cache"
+            " WHERE media_id = ?"
+        )
+
+        def _delete_url_cache_txn(txn):
+            txn.executemany(sql, [(media_id,) for media_id in media_ids])
+
+        return self.runInteraction("delete_url_cache", _delete_url_cache_txn)
+
+    def get_url_cache_media_before(self, before_ts):
+        sql = (
+            "SELECT media_id FROM local_media_repository"
+            " WHERE created_ts < ? AND url_cache IS NOT NULL"
+            " ORDER BY created_ts ASC"
+            " LIMIT 500"
+        )
+
+        def _get_url_cache_media_before_txn(txn):
+            txn.execute(sql, (before_ts,))
+            return [row[0] for row in txn]
+
+        return self.runInteraction(
+            "get_url_cache_media_before", _get_url_cache_media_before_txn,
+        )
+
+    def delete_url_cache_media(self, media_ids):
+        def _delete_url_cache_media_txn(txn):
+            sql = (
+                "DELETE FROM local_media_repository"
+                " WHERE media_id = ?"
+            )
+
+            txn.executemany(sql, [(media_id,) for media_id in media_ids])
+
+            sql = (
+                "DELETE FROM local_media_repository_thumbnails"
+                " WHERE media_id = ?"
+            )
+
+            txn.executemany(sql, [(media_id,) for media_id in media_ids])
+
+        return self.runInteraction(
+            "delete_url_cache_media", _delete_url_cache_media_txn,
+        )
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 72b670b83b..ccaaabcfa0 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -25,7 +25,7 @@ logger = logging.getLogger(__name__)
 
 # Remember to update this number every time a change is made to database
 # schema files, so the users will be informed on server restarts.
-SCHEMA_VERSION = 43
+SCHEMA_VERSION = 45
 
 dir_path = os.path.abspath(os.path.dirname(__file__))
 
diff --git a/synapse/storage/profile.py b/synapse/storage/profile.py
index 26a40905ae..beea3102fc 100644
--- a/synapse/storage/profile.py
+++ b/synapse/storage/profile.py
@@ -13,6 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from twisted.internet import defer
+
 from ._base import SQLBaseStore
 
 
@@ -55,3 +57,99 @@ class ProfileStore(SQLBaseStore):
             updatevalues={"avatar_url": new_avatar_url},
             desc="set_profile_avatar_url",
         )
+
+    def get_from_remote_profile_cache(self, user_id):
+        return self._simple_select_one(
+            table="remote_profile_cache",
+            keyvalues={"user_id": user_id},
+            retcols=("displayname", "avatar_url",),
+            allow_none=True,
+            desc="get_from_remote_profile_cache",
+        )
+
+    def add_remote_profile_cache(self, user_id, displayname, avatar_url):
+        """Ensure we are caching the remote user's profiles.
+
+        This should only be called when `is_subscribed_remote_profile_for_user`
+        would return true for the user.
+        """
+        return self._simple_upsert(
+            table="remote_profile_cache",
+            keyvalues={"user_id": user_id},
+            values={
+                "displayname": displayname,
+                "avatar_url": avatar_url,
+                "last_check": self._clock.time_msec(),
+            },
+            desc="add_remote_profile_cache",
+        )
+
+    def update_remote_profile_cache(self, user_id, displayname, avatar_url):
+        return self._simple_update(
+            table="remote_profile_cache",
+            keyvalues={"user_id": user_id},
+            values={
+                "displayname": displayname,
+                "avatar_url": avatar_url,
+                "last_check": self._clock.time_msec(),
+            },
+            desc="update_remote_profile_cache",
+        )
+
+    @defer.inlineCallbacks
+    def maybe_delete_remote_profile_cache(self, user_id):
+        """Check if we still care about the remote user's profile, and if we
+        don't then remove their profile from the cache
+        """
+        subscribed = yield self.is_subscribed_remote_profile_for_user(user_id)
+        if not subscribed:
+            yield self._simple_delete(
+                table="remote_profile_cache",
+                keyvalues={"user_id": user_id},
+                desc="delete_remote_profile_cache",
+            )
+
+    def get_remote_profile_cache_entries_that_expire(self, last_checked):
+        """Get all users who haven't been checked since `last_checked`
+        """
+        def _get_remote_profile_cache_entries_that_expire_txn(txn):
+            sql = """
+                SELECT user_id, displayname, avatar_url
+                FROM remote_profile_cache
+                WHERE last_check < ?
+            """
+
+            txn.execute(sql, (last_checked,))
+
+            return self.cursor_to_dict(txn)
+
+        return self.runInteraction(
+            "get_remote_profile_cache_entries_that_expire",
+            _get_remote_profile_cache_entries_that_expire_txn,
+        )
+
+    @defer.inlineCallbacks
+    def is_subscribed_remote_profile_for_user(self, user_id):
+        """Check whether we are interested in a remote user's profile.
+        """
+        res = yield self._simple_select_one_onecol(
+            table="group_users",
+            keyvalues={"user_id": user_id},
+            retcol="user_id",
+            allow_none=True,
+            desc="should_update_remote_profile_cache_for_user",
+        )
+
+        if res:
+            defer.returnValue(True)
+
+        res = yield self._simple_select_one_onecol(
+            table="group_invites",
+            keyvalues={"user_id": user_id},
+            retcol="user_id",
+            allow_none=True,
+            desc="should_update_remote_profile_cache_for_user",
+        )
+
+        if res:
+            defer.returnValue(True)
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 457ca288d0..a0fc9a6867 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -533,6 +533,46 @@ class RoomMemberStore(SQLBaseStore):
 
         defer.returnValue(True)
 
+    @cachedInlineCallbacks()
+    def was_host_joined(self, room_id, host):
+        """Check whether the server is or ever was in the room.
+
+        Args:
+            room_id (str)
+            host (str)
+
+        Returns:
+            Deferred: Resolves to True if the host is/was in the room, otherwise
+            False.
+        """
+        if '%' in host or '_' in host:
+            raise Exception("Invalid host name")
+
+        sql = """
+            SELECT user_id FROM room_memberships
+            WHERE room_id = ?
+                AND user_id LIKE ?
+                AND membership = 'join'
+            LIMIT 1
+        """
+
+        # We do need to be careful to ensure that host doesn't have any wild cards
+        # in it, but we checked above for known ones and we'll check below that
+        # the returned user actually has the correct domain.
+        like_clause = "%:" + host
+
+        rows = yield self._execute("was_host_joined", None, sql, room_id, like_clause)
+
+        if not rows:
+            defer.returnValue(False)
+
+        user_id = rows[0][0]
+        if get_domain_from_id(user_id) != host:
+            # This can only happen if the host name has something funky in it
+            raise Exception("Invalid host name")
+
+        defer.returnValue(True)
+
     def get_joined_hosts(self, room_id, state_entry):
         state_group = state_entry.state_group
         if not state_group:
diff --git a/synapse/storage/schema/delta/44/expire_url_cache.sql b/synapse/storage/schema/delta/44/expire_url_cache.sql
new file mode 100644
index 0000000000..e2b775f038
--- /dev/null
+++ b/synapse/storage/schema/delta/44/expire_url_cache.sql
@@ -0,0 +1,38 @@
+/* Copyright 2017 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CREATE INDEX local_media_repository_url_idx ON local_media_repository(created_ts) WHERE url_cache IS NOT NULL;
+
+-- we need to change `expires` to `expires_ts` so that we can index on it. SQLite doesn't support
+-- indices on expressions until 3.9.
+CREATE TABLE local_media_repository_url_cache_new(
+    url TEXT,
+    response_code INTEGER,
+    etag TEXT,
+    expires_ts BIGINT,
+    og TEXT,
+    media_id TEXT,
+    download_ts BIGINT
+);
+
+INSERT INTO local_media_repository_url_cache_new
+    SELECT url, response_code, etag, expires + download_ts, og, media_id, download_ts FROM local_media_repository_url_cache;
+
+DROP TABLE local_media_repository_url_cache;
+ALTER TABLE local_media_repository_url_cache_new RENAME TO local_media_repository_url_cache;
+
+CREATE INDEX local_media_repository_url_cache_expires_idx ON local_media_repository_url_cache(expires_ts);
+CREATE INDEX local_media_repository_url_cache_by_url_download_ts ON local_media_repository_url_cache(url, download_ts);
+CREATE INDEX local_media_repository_url_cache_media_idx ON local_media_repository_url_cache(media_id);
diff --git a/synapse/storage/schema/delta/45/group_server.sql b/synapse/storage/schema/delta/45/group_server.sql
new file mode 100644
index 0000000000..b2333848a0
--- /dev/null
+++ b/synapse/storage/schema/delta/45/group_server.sql
@@ -0,0 +1,167 @@
+/* Copyright 2017 Vector Creations Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CREATE TABLE groups (
+    group_id TEXT NOT NULL,
+    name TEXT,  -- the display name of the room
+    avatar_url TEXT,
+    short_description TEXT,
+    long_description TEXT
+);
+
+CREATE UNIQUE INDEX groups_idx ON groups(group_id);
+
+
+-- list of users the group server thinks are joined
+CREATE TABLE group_users (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    is_admin BOOLEAN NOT NULL,
+    is_public BOOLEAN NOT NULL  -- whether the users membership can be seen by everyone
+);
+
+
+CREATE INDEX groups_users_g_idx ON group_users(group_id, user_id);
+CREATE INDEX groups_users_u_idx ON group_users(user_id);
+
+-- list of users the group server thinks are invited
+CREATE TABLE group_invites (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL
+);
+
+CREATE INDEX groups_invites_g_idx ON group_invites(group_id, user_id);
+CREATE INDEX groups_invites_u_idx ON group_invites(user_id);
+
+
+CREATE TABLE group_rooms (
+    group_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    is_public BOOLEAN NOT NULL  -- whether the room can be seen by everyone
+);
+
+CREATE UNIQUE INDEX groups_rooms_g_idx ON group_rooms(group_id, room_id);
+CREATE INDEX groups_rooms_r_idx ON group_rooms(room_id);
+
+
+-- Rooms to include in the summary
+CREATE TABLE group_summary_rooms (
+    group_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    category_id TEXT NOT NULL,
+    room_order BIGINT NOT NULL,
+    is_public BOOLEAN NOT NULL, -- whether the room should be show to everyone
+    UNIQUE (group_id, category_id, room_id, room_order),
+    CHECK (room_order > 0)
+);
+
+CREATE UNIQUE INDEX group_summary_rooms_g_idx ON group_summary_rooms(group_id, room_id, category_id);
+
+
+-- Categories to include in the summary
+CREATE TABLE group_summary_room_categories (
+    group_id TEXT NOT NULL,
+    category_id TEXT NOT NULL,
+    cat_order BIGINT NOT NULL,
+    UNIQUE (group_id, category_id, cat_order),
+    CHECK (cat_order > 0)
+);
+
+-- The categories in the group
+CREATE TABLE group_room_categories (
+    group_id TEXT NOT NULL,
+    category_id TEXT NOT NULL,
+    profile TEXT NOT NULL,
+    is_public BOOLEAN NOT NULL, -- whether the category should be show to everyone
+    UNIQUE (group_id, category_id)
+);
+
+-- The users to include in the group summary
+CREATE TABLE group_summary_users (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    role_id TEXT NOT NULL,
+    user_order BIGINT NOT NULL,
+    is_public BOOLEAN NOT NULL  -- whether the user should be show to everyone
+);
+
+CREATE INDEX group_summary_users_g_idx ON group_summary_users(group_id);
+
+-- The roles to include in the group summary
+CREATE TABLE group_summary_roles (
+    group_id TEXT NOT NULL,
+    role_id TEXT NOT NULL,
+    role_order BIGINT NOT NULL,
+    UNIQUE (group_id, role_id, role_order),
+    CHECK (role_order > 0)
+);
+
+
+-- The roles in a groups
+CREATE TABLE group_roles (
+    group_id TEXT NOT NULL,
+    role_id TEXT NOT NULL,
+    profile TEXT NOT NULL,
+    is_public BOOLEAN NOT NULL,  -- whether the role should be show to everyone
+    UNIQUE (group_id, role_id)
+);
+
+
+-- List of  attestations we've given out and need to renew
+CREATE TABLE group_attestations_renewals (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    valid_until_ms BIGINT NOT NULL
+);
+
+CREATE INDEX group_attestations_renewals_g_idx ON group_attestations_renewals(group_id, user_id);
+CREATE INDEX group_attestations_renewals_u_idx ON group_attestations_renewals(user_id);
+CREATE INDEX group_attestations_renewals_v_idx ON group_attestations_renewals(valid_until_ms);
+
+
+-- List of attestations we've received from remotes and are interested in.
+CREATE TABLE group_attestations_remote (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    valid_until_ms BIGINT NOT NULL,
+    attestation_json TEXT NOT NULL
+);
+
+CREATE INDEX group_attestations_remote_g_idx ON group_attestations_remote(group_id, user_id);
+CREATE INDEX group_attestations_remote_u_idx ON group_attestations_remote(user_id);
+CREATE INDEX group_attestations_remote_v_idx ON group_attestations_remote(valid_until_ms);
+
+
+-- The group membership for the HS's users
+CREATE TABLE local_group_membership (
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    is_admin BOOLEAN NOT NULL,
+    membership TEXT NOT NULL,
+    is_publicised BOOLEAN NOT NULL,  -- if the user is publicising their membership
+    content TEXT NOT NULL
+);
+
+CREATE INDEX local_group_membership_u_idx ON local_group_membership(user_id, group_id);
+CREATE INDEX local_group_membership_g_idx ON local_group_membership(group_id);
+
+
+CREATE TABLE local_group_updates (
+    stream_id BIGINT NOT NULL,
+    group_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    type TEXT NOT NULL,
+    content TEXT NOT NULL
+);
diff --git a/synapse/storage/schema/delta/45/profile_cache.sql b/synapse/storage/schema/delta/45/profile_cache.sql
new file mode 100644
index 0000000000..e5ddc84df0
--- /dev/null
+++ b/synapse/storage/schema/delta/45/profile_cache.sql
@@ -0,0 +1,28 @@
+/* Copyright 2017 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+-- A subset of remote users whose profiles we have cached.
+-- Whether a user is in this table or not is defined by the storage function
+-- `is_subscribed_remote_profile_for_user`
+CREATE TABLE remote_profile_cache (
+    user_id TEXT NOT NULL,
+    displayname TEXT,
+    avatar_url TEXT,
+    last_check BIGINT NOT NULL
+);
+
+CREATE UNIQUE INDEX remote_profile_cache_user_id ON remote_profile_cache(user_id);
+CREATE INDEX remote_profile_cache_time ON remote_profile_cache(last_check);
diff --git a/synapse/streams/events.py b/synapse/streams/events.py
index 91a59b0bae..f03ad99118 100644
--- a/synapse/streams/events.py
+++ b/synapse/streams/events.py
@@ -45,6 +45,7 @@ class EventSources(object):
         push_rules_key, _ = self.store.get_push_rules_stream_token()
         to_device_key = self.store.get_to_device_stream_token()
         device_list_key = self.store.get_device_stream_token()
+        groups_key = self.store.get_group_stream_token()
 
         token = StreamToken(
             room_key=(
@@ -65,6 +66,7 @@ class EventSources(object):
             push_rules_key=push_rules_key,
             to_device_key=to_device_key,
             device_list_key=device_list_key,
+            groups_key=groups_key,
         )
         defer.returnValue(token)
 
@@ -73,6 +75,7 @@ class EventSources(object):
         push_rules_key, _ = self.store.get_push_rules_stream_token()
         to_device_key = self.store.get_to_device_stream_token()
         device_list_key = self.store.get_device_stream_token()
+        groups_key = self.store.get_group_stream_token()
 
         token = StreamToken(
             room_key=(
@@ -93,5 +96,6 @@ class EventSources(object):
             push_rules_key=push_rules_key,
             to_device_key=to_device_key,
             device_list_key=device_list_key,
+            groups_key=groups_key,
         )
         defer.returnValue(token)
diff --git a/synapse/types.py b/synapse/types.py
index 111948540d..37d5fa7f9f 100644
--- a/synapse/types.py
+++ b/synapse/types.py
@@ -156,6 +156,11 @@ class EventID(DomainSpecificString):
     SIGIL = "$"
 
 
+class GroupID(DomainSpecificString):
+    """Structure representing a group ID."""
+    SIGIL = "+"
+
+
 class StreamToken(
     namedtuple("Token", (
         "room_key",
@@ -166,6 +171,7 @@ class StreamToken(
         "push_rules_key",
         "to_device_key",
         "device_list_key",
+        "groups_key",
     ))
 ):
     _SEPARATOR = "_"
@@ -204,6 +210,7 @@ class StreamToken(
             or (int(other.push_rules_key) < int(self.push_rules_key))
             or (int(other.to_device_key) < int(self.to_device_key))
             or (int(other.device_list_key) < int(self.device_list_key))
+            or (int(other.groups_key) < int(self.groups_key))
         )
 
     def copy_and_advance(self, key, new_value):
diff --git a/synapse/util/async.py b/synapse/util/async.py
index 1453faf0ef..a0a9039475 100644
--- a/synapse/util/async.py
+++ b/synapse/util/async.py
@@ -19,7 +19,7 @@ from twisted.internet import defer, reactor
 from .logcontext import (
     PreserveLoggingContext, preserve_fn, preserve_context_over_deferred,
 )
-from synapse.util import unwrapFirstError
+from synapse.util import logcontext, unwrapFirstError
 
 from contextlib import contextmanager
 
@@ -53,6 +53,11 @@ class ObservableDeferred(object):
 
     Cancelling or otherwise resolving an observer will not affect the original
     ObservableDeferred.
+
+    NB that it does not attempt to do anything with logcontexts; in general
+    you should probably make_deferred_yieldable the deferreds
+    returned by `observe`, and ensure that the original deferred runs its
+    callbacks in the sentinel logcontext.
     """
 
     __slots__ = ["_deferred", "_observers", "_result"]
@@ -155,7 +160,7 @@ def concurrently_execute(func, args, limit):
         except StopIteration:
             pass
 
-    return preserve_context_over_deferred(defer.gatherResults([
+    return logcontext.make_deferred_yieldable(defer.gatherResults([
         preserve_fn(_concurrently_execute_inner)()
         for _ in xrange(limit)
     ], consumeErrors=True)).addErrback(unwrapFirstError)
@@ -203,7 +208,26 @@ class Linearizer(object):
             except:
                 logger.exception("Unexpected exception in Linearizer")
 
-        logger.info("Acquired linearizer lock %r for key %r", self.name, key)
+            logger.info("Acquired linearizer lock %r for key %r", self.name,
+                        key)
+
+            # if the code holding the lock completes synchronously, then it
+            # will recursively run the next claimant on the list. That can
+            # relatively rapidly lead to stack exhaustion. This is essentially
+            # the same problem as http://twistedmatrix.com/trac/ticket/9304.
+            #
+            # In order to break the cycle, we add a cheeky sleep(0) here to
+            # ensure that we fall back to the reactor between each iteration.
+            #
+            # (There's no particular need for it to happen before we return
+            # the context manager, but it needs to happen while we hold the
+            # lock, and the context manager's exit code must be synchronous,
+            # so actually this is the only sensible place.
+            yield run_on_reactor()
+
+        else:
+            logger.info("Acquired uncontended linearizer lock %r for key %r",
+                        self.name, key)
 
         @contextmanager
         def _ctx_manager():
@@ -211,7 +235,8 @@ class Linearizer(object):
                 yield
             finally:
                 logger.info("Releasing linearizer lock %r for key %r", self.name, key)
-                new_defer.callback(None)
+                with PreserveLoggingContext():
+                    new_defer.callback(None)
                 current_d = self.key_to_defer.get(key)
                 if current_d is new_defer:
                     self.key_to_defer.pop(key, None)
diff --git a/synapse/util/logformatter.py b/synapse/util/logformatter.py
new file mode 100644
index 0000000000..cdbc4bffd7
--- /dev/null
+++ b/synapse/util/logformatter.py
@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import StringIO
+import logging
+import traceback
+
+
+class LogFormatter(logging.Formatter):
+    """Log formatter which gives more detail for exceptions
+
+    This is the same as the standard log formatter, except that when logging
+    exceptions [typically via log.foo("msg", exc_info=1)], it prints the
+    sequence that led up to the point at which the exception was caught.
+    (Normally only stack frames between the point the exception was raised and
+    where it was caught are logged).
+    """
+    def __init__(self, *args, **kwargs):
+        super(LogFormatter, self).__init__(*args, **kwargs)
+
+    def formatException(self, ei):
+        sio = StringIO.StringIO()
+        (typ, val, tb) = ei
+
+        # log the stack above the exception capture point if possible, but
+        # check that we actually have an f_back attribute to work around
+        # https://twistedmatrix.com/trac/ticket/9305
+
+        if tb and hasattr(tb.tb_frame, 'f_back'):
+            sio.write("Capture point (most recent call last):\n")
+            traceback.print_stack(tb.tb_frame.f_back, None, sio)
+
+        traceback.print_exception(typ, val, tb, None, sio)
+        s = sio.getvalue()
+        sio.close()
+        if s[-1:] == "\n":
+            s = s[:-1]
+        return s
diff --git a/synapse/util/module_loader.py b/synapse/util/module_loader.py
new file mode 100644
index 0000000000..4288312b8a
--- /dev/null
+++ b/synapse/util/module_loader.py
@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import importlib
+
+from synapse.config._base import ConfigError
+
+
+def load_module(provider):
+    """ Loads a module with its config
+    Take a dict with keys 'module' (the module name) and 'config'
+    (the config dict).
+
+    Returns
+        Tuple of (provider class, parsed config object)
+    """
+    # We need to import the module, and then pick the class out of
+    # that, so we split based on the last dot.
+    module, clz = provider['module'].rsplit(".", 1)
+    module = importlib.import_module(module)
+    provider_class = getattr(module, clz)
+
+    try:
+        provider_config = provider_class.parse_config(provider["config"])
+    except Exception as e:
+        raise ConfigError(
+            "Failed to parse config for %r: %r" % (provider['module'], e)
+        )
+
+    return provider_class, provider_config
diff --git a/tests/handlers/test_profile.py b/tests/handlers/test_profile.py
index 2a203129ca..a5f47181d7 100644
--- a/tests/handlers/test_profile.py
+++ b/tests/handlers/test_profile.py
@@ -62,8 +62,6 @@ class ProfileTestCase(unittest.TestCase):
         self.ratelimiter = hs.get_ratelimiter()
         self.ratelimiter.send_message.return_value = (True, 0)
 
-        hs.handlers = ProfileHandlers(hs)
-
         self.store = hs.get_datastore()
 
         self.frank = UserID.from_string("@1234ABCD:test")
@@ -72,7 +70,7 @@ class ProfileTestCase(unittest.TestCase):
 
         yield self.store.create_profile(self.frank.localpart)
 
-        self.handler = hs.get_handlers().profile_handler
+        self.handler = hs.get_profile_handler()
 
     @defer.inlineCallbacks
     def test_get_my_name(self):
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index c8cf9a63ec..e990e45220 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -40,13 +40,14 @@ class RegistrationTestCase(unittest.TestCase):
         self.hs = yield setup_test_homeserver(
             handlers=None,
             http_client=None,
-            expire_access_token=True)
+            expire_access_token=True,
+            profile_handler=Mock(),
+        )
         self.macaroon_generator = Mock(
             generate_access_token=Mock(return_value='secret'))
         self.hs.get_macaroon_generator = Mock(return_value=self.macaroon_generator)
         self.hs.handlers = RegistrationHandlers(self.hs)
         self.handler = self.hs.get_handlers().registration_handler
-        self.hs.get_handlers().profile_handler = Mock()
 
     @defer.inlineCallbacks
     def test_user_is_created_and_logged_in_if_doesnt_exist(self):
diff --git a/tests/rest/client/v1/test_profile.py b/tests/rest/client/v1/test_profile.py
index 1e95e97538..dddcf51b69 100644
--- a/tests/rest/client/v1/test_profile.py
+++ b/tests/rest/client/v1/test_profile.py
@@ -46,6 +46,7 @@ class ProfileTestCase(unittest.TestCase):
             resource_for_client=self.mock_resource,
             federation=Mock(),
             replication_layer=Mock(),
+            profile_handler=self.mock_handler
         )
 
         def _get_user_by_req(request=None, allow_guest=False):
@@ -53,8 +54,6 @@ class ProfileTestCase(unittest.TestCase):
 
         hs.get_v1auth().get_user_by_req = _get_user_by_req
 
-        hs.get_handlers().profile_handler = self.mock_handler
-
         profile.register_servlets(hs, self.mock_resource)
 
     @defer.inlineCallbacks
diff --git a/tests/rest/client/v1/test_rooms.py b/tests/rest/client/v1/test_rooms.py
index d746ea8568..de376fb514 100644
--- a/tests/rest/client/v1/test_rooms.py
+++ b/tests/rest/client/v1/test_rooms.py
@@ -1032,7 +1032,7 @@ class RoomMessageListTestCase(RestTestCase):
 
     @defer.inlineCallbacks
     def test_topo_token_is_accepted(self):
-        token = "t1-0_0_0_0_0_0_0_0"
+        token = "t1-0_0_0_0_0_0_0_0_0"
         (code, response) = yield self.mock_resource.trigger_get(
             "/rooms/%s/messages?access_token=x&from=%s" %
             (self.room_id, token))
@@ -1044,7 +1044,7 @@ class RoomMessageListTestCase(RestTestCase):
 
     @defer.inlineCallbacks
     def test_stream_token_is_accepted_for_fwd_pagianation(self):
-        token = "s0_0_0_0_0_0_0_0"
+        token = "s0_0_0_0_0_0_0_0_0"
         (code, response) = yield self.mock_resource.trigger_get(
             "/rooms/%s/messages?access_token=x&from=%s" %
             (self.room_id, token))
diff --git a/tests/rest/client/v2_alpha/test_register.py b/tests/rest/client/v2_alpha/test_register.py
index b6173ab2ee..821c735528 100644
--- a/tests/rest/client/v2_alpha/test_register.py
+++ b/tests/rest/client/v2_alpha/test_register.py
@@ -47,6 +47,7 @@ class RegisterRestServletTestCase(unittest.TestCase):
         self.hs.get_auth_handler = Mock(return_value=self.auth_handler)
         self.hs.get_device_handler = Mock(return_value=self.device_handler)
         self.hs.config.enable_registration = True
+        self.hs.config.auto_join_rooms = []
 
         # init the thing we're testing
         self.servlet = RegisterRestServlet(self.hs)
diff --git a/tests/storage/event_injector.py b/tests/storage/event_injector.py
deleted file mode 100644
index 024ac15069..0000000000
--- a/tests/storage/event_injector.py
+++ /dev/null
@@ -1,76 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2015, 2016 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-
-from twisted.internet import defer
-
-from synapse.api.constants import EventTypes
-
-
-class EventInjector:
-    def __init__(self, hs):
-        self.hs = hs
-        self.store = hs.get_datastore()
-        self.message_handler = hs.get_handlers().message_handler
-        self.event_builder_factory = hs.get_event_builder_factory()
-
-    @defer.inlineCallbacks
-    def create_room(self, room, user):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Create,
-            "sender": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
-
-    @defer.inlineCallbacks
-    def inject_room_member(self, room, user, membership):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Member,
-            "sender": user.to_string(),
-            "state_key": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {"membership": membership},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
-
-        defer.returnValue(event)
-
-    @defer.inlineCallbacks
-    def inject_message(self, room, user, body):
-        builder = self.event_builder_factory.new({
-            "type": EventTypes.Message,
-            "sender": user.to_string(),
-            "state_key": user.to_string(),
-            "room_id": room.to_string(),
-            "content": {"body": body, "msgtype": u"message"},
-        })
-
-        event, context = yield self.message_handler._create_new_client_event(
-            builder
-        )
-
-        yield self.store.persist_event(event, context)
diff --git a/tests/util/test_linearizer.py b/tests/util/test_linearizer.py
index afcba482f9..793a88e462 100644
--- a/tests/util/test_linearizer.py
+++ b/tests/util/test_linearizer.py
@@ -12,8 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
-
+from synapse.util import async, logcontext
 from tests import unittest
 
 from twisted.internet import defer
@@ -38,7 +37,28 @@ class LinearizerTestCase(unittest.TestCase):
         with cm1:
             self.assertFalse(d2.called)
 
-        self.assertTrue(d2.called)
-
         with (yield d2):
             pass
+
+    def test_lots_of_queued_things(self):
+        # we have one slow thing, and lots of fast things queued up behind it.
+        # it should *not* explode the stack.
+        linearizer = Linearizer()
+
+        @defer.inlineCallbacks
+        def func(i, sleep=False):
+            with logcontext.LoggingContext("func(%s)" % i) as lc:
+                with (yield linearizer.queue("")):
+                    self.assertEqual(
+                        logcontext.LoggingContext.current_context(), lc)
+                    if sleep:
+                        yield async.sleep(0)
+
+                self.assertEqual(
+                    logcontext.LoggingContext.current_context(), lc)
+
+        func(0, sleep=True)
+        for i in xrange(1, 100):
+            func(i)
+
+        return func(1000)
diff --git a/tests/util/test_log_context.py b/tests/util/test_logcontext.py
index 9ffe209c4d..e2f7765f49 100644
--- a/tests/util/test_log_context.py
+++ b/tests/util/test_logcontext.py
@@ -94,3 +94,41 @@ class LoggingContextTestCase(unittest.TestCase):
                 yield defer.succeed(None)
 
         return self._test_preserve_fn(nonblocking_function)
+
+    @defer.inlineCallbacks
+    def test_make_deferred_yieldable(self):
+        # a function which retuns an incomplete deferred, but doesn't follow
+        # the synapse rules.
+        def blocking_function():
+            d = defer.Deferred()
+            reactor.callLater(0, d.callback, None)
+            return d
+
+        sentinel_context = LoggingContext.current_context()
+
+        with LoggingContext() as context_one:
+            context_one.test_key = "one"
+
+            d1 = logcontext.make_deferred_yieldable(blocking_function())
+            # make sure that the context was reset by make_deferred_yieldable
+            self.assertIs(LoggingContext.current_context(), sentinel_context)
+
+            yield d1
+
+            # now it should be restored
+            self._check_test_key("one")
+
+    @defer.inlineCallbacks
+    def test_make_deferred_yieldable_on_non_deferred(self):
+        """Check that make_deferred_yieldable does the right thing when its
+        argument isn't actually a deferred"""
+
+        with LoggingContext() as context_one:
+            context_one.test_key = "one"
+
+            d1 = logcontext.make_deferred_yieldable("bum")
+            self._check_test_key("one")
+
+            r = yield d1
+            self.assertEqual(r, "bum")
+            self._check_test_key("one")