diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index eb15d8c54..e4e3d1c59 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -147,6 +147,10 @@ class FilterCollection(object):
             self.filter_json.get("room", {}).get("ephemeral", {})
         )
 
+        self.room_private_user_data = Filter(
+            self.filter_json.get("room", {}).get("private_user_data", {})
+        )
+
         self.presence_filter = Filter(
             self.filter_json.get("presence", {})
         )
@@ -172,6 +176,9 @@ class FilterCollection(object):
     def filter_room_ephemeral(self, events):
         return self.room_ephemeral_filter.filter(events)
 
+    def filter_room_private_user_data(self, events):
+        return self.room_private_user_data.filter(events)
+
 
 class Filter(object):
     def __init__(self, filter_json):
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 024474d5f..0f947993d 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -322,6 +322,8 @@ class MessageHandler(BaseHandler):
             user, pagination_config.get_source_config("receipt"), None
         )
 
+        tags_by_room = yield self.store.get_tags_for_user(user_id)
+
         public_room_ids = yield self.store.get_public_room_ids()
 
         limit = pagin_config.limit
@@ -398,6 +400,15 @@ class MessageHandler(BaseHandler):
                     serialize_event(c, time_now, as_client_event)
                     for c in current_state.values()
                 ]
+
+                private_user_data = []
+                tags = tags_by_room.get(event.room_id)
+                if tags:
+                    private_user_data.append({
+                        "type": "m.tag",
+                        "content": {"tags": tags},
+                    })
+                d["private_user_data"] = private_user_data
             except:
                 logger.exception("Failed to get snapshot")
 
@@ -447,6 +458,16 @@ class MessageHandler(BaseHandler):
             result = yield self._room_initial_sync_parted(
                 user_id, room_id, pagin_config, member_event
             )
+
+        private_user_data = []
+        tags = yield self.store.get_tags_for_room(user_id, room_id)
+        if tags:
+            private_user_data.append({
+                "type": "m.tag",
+                "content": {"tags": tags},
+            })
+        result["private_user_data"] = private_user_data
+
         defer.returnValue(result)
 
     @defer.inlineCallbacks
@@ -476,8 +497,8 @@ class MessageHandler(BaseHandler):
             user_id, messages
         )
 
-        start_token = StreamToken(token[0], 0, 0, 0)
-        end_token = StreamToken(token[1], 0, 0, 0)
+        start_token = StreamToken(token[0], 0, 0, 0, 0)
+        end_token = StreamToken(token[1], 0, 0, 0, 0)
 
         time_now = self.clock.time_msec()
 
diff --git a/synapse/handlers/private_user_data.py b/synapse/handlers/private_user_data.py
new file mode 100644
index 000000000..1778c7132
--- /dev/null
+++ b/synapse/handlers/private_user_data.py
@@ -0,0 +1,46 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 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
+
+
+class PrivateUserDataEventSource(object):
+    def __init__(self, hs):
+        self.store = hs.get_datastore()
+
+    def get_current_key(self, direction='f'):
+        return self.store.get_max_private_user_data_stream_id()
+
+    @defer.inlineCallbacks
+    def get_new_events_for_user(self, user, from_key, limit):
+        user_id = user.to_string()
+        last_stream_id = from_key
+
+        current_stream_id = yield self.store.get_max_private_user_data_stream_id()
+        tags = yield self.store.get_updated_tags(user_id, last_stream_id)
+
+        results = []
+        for room_id, room_tags in tags.items():
+            results.append({
+                "type": "m.tag",
+                "content": {"tags": room_tags},
+                "room_id": room_id,
+            })
+
+        defer.returnValue((results, current_stream_id))
+
+    @defer.inlineCallbacks
+    def get_pagination_rows(self, user, config, key):
+        defer.returnValue(([], config.to_id))
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 19c4d5163..d6527c1ae 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -51,6 +51,7 @@ class JoinedSyncResult(collections.namedtuple("JoinedSyncResult", [
     "timeline",
     "state",
     "ephemeral",
+    "private_user_data",
 ])):
     __slots__ = []
 
@@ -58,13 +59,19 @@ class JoinedSyncResult(collections.namedtuple("JoinedSyncResult", [
         """Make the result appear empty if there are no updates. This is used
         to tell if room needs to be part of the sync result.
         """
-        return bool(self.timeline or self.state or self.ephemeral)
+        return bool(
+            self.timeline
+            or self.state
+            or self.ephemeral
+            or self.private_user_data
+        )
 
 
 class ArchivedSyncResult(collections.namedtuple("JoinedSyncResult", [
     "room_id",
     "timeline",
     "state",
+    "private_user_data",
 ])):
     __slots__ = []
 
@@ -72,7 +79,11 @@ class ArchivedSyncResult(collections.namedtuple("JoinedSyncResult", [
         """Make the result appear empty if there are no updates. This is used
         to tell if room needs to be part of the sync result.
         """
-        return bool(self.timeline or self.state)
+        return bool(
+            self.timeline
+            or self.state
+            or self.private_user_data
+        )
 
 
 class InvitedSyncResult(collections.namedtuple("InvitedSyncResult", [
@@ -197,6 +208,10 @@ class SyncHandler(BaseHandler):
             )
         )
 
+        tags_by_room = yield self.store.get_tags_for_user(
+            sync_config.user.to_string()
+        )
+
         joined = []
         invited = []
         archived = []
@@ -208,6 +223,7 @@ class SyncHandler(BaseHandler):
                     now_token=now_token,
                     timeline_since_token=timeline_since_token,
                     ephemeral_by_room=ephemeral_by_room,
+                    tags_by_room=tags_by_room,
                 )
                 joined.append(room_sync)
             elif event.membership == Membership.INVITE:
@@ -226,6 +242,7 @@ class SyncHandler(BaseHandler):
                     leave_event_id=event.event_id,
                     leave_token=leave_token,
                     timeline_since_token=timeline_since_token,
+                    tags_by_room=tags_by_room,
                 )
                 archived.append(room_sync)
 
@@ -240,7 +257,7 @@ class SyncHandler(BaseHandler):
     @defer.inlineCallbacks
     def full_state_sync_for_joined_room(self, room_id, sync_config,
                                         now_token, timeline_since_token,
-                                        ephemeral_by_room):
+                                        ephemeral_by_room, tags_by_room):
         """Sync a room for a client which is starting without any state
         Returns:
             A Deferred JoinedSyncResult.
@@ -260,8 +277,21 @@ class SyncHandler(BaseHandler):
             timeline=batch,
             state=current_state_events,
             ephemeral=ephemeral_by_room.get(room_id, []),
+            private_user_data=self.private_user_data_for_room(
+                room_id, tags_by_room
+            ),
         ))
 
+    def private_user_data_for_room(self, room_id, tags_by_room):
+        private_user_data = []
+        tags = tags_by_room.get(room_id)
+        if tags:
+            private_user_data.append({
+                "type": "m.tag",
+                "content": {"tags": tags},
+            })
+        return private_user_data
+
     @defer.inlineCallbacks
     def ephemeral_by_room(self, sync_config, now_token, since_token=None):
         """Get the ephemeral events for each room the user is in
@@ -311,7 +341,7 @@ class SyncHandler(BaseHandler):
     @defer.inlineCallbacks
     def full_state_sync_for_archived_room(self, room_id, sync_config,
                                           leave_event_id, leave_token,
-                                          timeline_since_token):
+                                          timeline_since_token, tags_by_room):
         """Sync a room for a client which is starting without any state
         Returns:
             A Deferred JoinedSyncResult.
@@ -329,6 +359,9 @@ class SyncHandler(BaseHandler):
             room_id=room_id,
             timeline=batch,
             state=leave_state[leave_event_id].values(),
+            private_user_data=self.private_user_data_for_room(
+                room_id, tags_by_room
+            ),
         ))
 
     @defer.inlineCallbacks
@@ -374,6 +407,11 @@ class SyncHandler(BaseHandler):
             limit=timeline_limit + 1,
         )
 
+        tags_by_room = yield self.store.get_updated_tags(
+            sync_config.user.to_string(),
+            since_token.private_user_data_key,
+        )
+
         joined = []
         archived = []
         if len(room_events) <= timeline_limit:
@@ -414,7 +452,10 @@ class SyncHandler(BaseHandler):
                         limited=limited,
                     ),
                     state=state,
-                    ephemeral=ephemeral_by_room.get(room_id, [])
+                    ephemeral=ephemeral_by_room.get(room_id, []),
+                    private_user_data=self.private_user_data_for_room(
+                        room_id, tags_by_room
+                    ),
                 )
                 if room_sync:
                     joined.append(room_sync)
@@ -431,14 +472,14 @@ class SyncHandler(BaseHandler):
             for room_id in joined_room_ids:
                 room_sync = yield self.incremental_sync_with_gap_for_room(
                     room_id, sync_config, since_token, now_token,
-                    ephemeral_by_room
+                    ephemeral_by_room, tags_by_room
                 )
                 if room_sync:
                     joined.append(room_sync)
 
         for leave_event in leave_events:
             room_sync = yield self.incremental_sync_for_archived_room(
-                sync_config, leave_event, since_token
+                sync_config, leave_event, since_token, tags_by_room
             )
             archived.append(room_sync)
 
@@ -502,7 +543,7 @@ class SyncHandler(BaseHandler):
     @defer.inlineCallbacks
     def incremental_sync_with_gap_for_room(self, room_id, sync_config,
                                            since_token, now_token,
-                                           ephemeral_by_room):
+                                           ephemeral_by_room, tags_by_room):
         """ Get the incremental delta needed to bring the client up to date for
         the room. Gives the client the most recent events and the changes to
         state.
@@ -543,7 +584,10 @@ class SyncHandler(BaseHandler):
             room_id=room_id,
             timeline=batch,
             state=state_events_delta,
-            ephemeral=ephemeral_by_room.get(room_id, [])
+            ephemeral=ephemeral_by_room.get(room_id, []),
+            private_user_data=self.private_user_data_for_room(
+                room_id, tags_by_room
+            ),
         )
 
         logging.debug("Room sync: %r", room_sync)
@@ -552,7 +596,7 @@ class SyncHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def incremental_sync_for_archived_room(self, sync_config, leave_event,
-                                           since_token):
+                                           since_token, tags_by_room):
         """ Get the incremental delta needed to bring the client up to date for
         the archived room.
         Returns:
@@ -593,6 +637,9 @@ class SyncHandler(BaseHandler):
             room_id=leave_event.room_id,
             timeline=batch,
             state=state_events_delta,
+            private_user_data=self.private_user_data_for_room(
+                leave_event.room_id, tags_by_room
+            ),
         )
 
         logging.debug("Room sync: %r", room_sync)
diff --git a/synapse/notifier.py b/synapse/notifier.py
index f998fc83b..a78ee3c1e 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -270,7 +270,7 @@ class Notifier(object):
 
     @defer.inlineCallbacks
     def wait_for_events(self, user, rooms, timeout, callback,
-                        from_token=StreamToken("s0", "0", "0", "0")):
+                        from_token=StreamToken("s0", "0", "0", "0", "0")):
         """Wait until the callback returns a non empty response or the
         timeout fires.
         """
diff --git a/synapse/rest/client/v2_alpha/__init__.py b/synapse/rest/client/v2_alpha/__init__.py
index 5831ff0e6..a10813234 100644
--- a/synapse/rest/client/v2_alpha/__init__.py
+++ b/synapse/rest/client/v2_alpha/__init__.py
@@ -22,6 +22,7 @@ from . import (
     receipts,
     keys,
     tokenrefresh,
+    tags,
 )
 
 from synapse.http.server import JsonResource
@@ -44,3 +45,4 @@ class ClientV2AlphaRestResource(JsonResource):
         receipts.register_servlets(hs, client_resource)
         keys.register_servlets(hs, client_resource)
         tokenrefresh.register_servlets(hs, client_resource)
+        tags.register_servlets(hs, client_resource)
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 1840eef77..32a1087c9 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -220,6 +220,10 @@ class SyncRestServlet(RestServlet):
             )
             timeline_event_ids.append(event.event_id)
 
+        private_user_data = filter.filter_room_private_user_data(
+            room.private_user_data
+        )
+
         result = {
             "event_map": event_map,
             "timeline": {
@@ -228,6 +232,7 @@ class SyncRestServlet(RestServlet):
                 "limited": room.timeline.limited,
             },
             "state": {"events": state_event_ids},
+            "private_user_data": {"events": private_user_data},
         }
 
         if joined:
diff --git a/synapse/rest/client/v2_alpha/tags.py b/synapse/rest/client/v2_alpha/tags.py
new file mode 100644
index 000000000..dcfe6bd20
--- /dev/null
+++ b/synapse/rest/client/v2_alpha/tags.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 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 client_v2_pattern
+
+from synapse.http.servlet import RestServlet
+from synapse.api.errors import AuthError, SynapseError
+
+from twisted.internet import defer
+
+import logging
+
+import simplejson as json
+
+logger = logging.getLogger(__name__)
+
+
+class TagListServlet(RestServlet):
+    """
+    GET /user/{user_id}/rooms/{room_id}/tags HTTP/1.1
+    """
+    PATTERN = client_v2_pattern(
+        "/user/(?P<user_id>[^/]*)/rooms/(?P<room_id>[^/]*)/tags"
+    )
+
+    def __init__(self, hs):
+        super(TagListServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, user_id, room_id):
+        auth_user, _ = yield self.auth.get_user_by_req(request)
+        if user_id != auth_user.to_string():
+            raise AuthError(403, "Cannot get tags for other users.")
+
+        tags = yield self.store.get_tags_for_room(user_id, room_id)
+
+        defer.returnValue((200, {"tags": tags}))
+
+
+class TagServlet(RestServlet):
+    """
+    PUT /user/{user_id}/rooms/{room_id}/tags/{tag} HTTP/1.1
+    DELETE /user/{user_id}/rooms/{room_id}/tags/{tag} HTTP/1.1
+    """
+    PATTERN = client_v2_pattern(
+        "/user/(?P<user_id>[^/]*)/rooms/(?P<room_id>[^/]*)/tags/(?P<tag>[^/]*)"
+    )
+
+    def __init__(self, hs):
+        super(TagServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+        self.notifier = hs.get_notifier()
+
+    @defer.inlineCallbacks
+    def on_PUT(self, request, user_id, room_id, tag):
+        auth_user, _ = yield self.auth.get_user_by_req(request)
+        if user_id != auth_user.to_string():
+            raise AuthError(403, "Cannot add tags for other users.")
+
+        try:
+            content_bytes = request.content.read()
+            body = json.loads(content_bytes)
+        except:
+            raise SynapseError(400, "Invalid tag JSON")
+
+        max_id = yield self.store.add_tag_to_room(user_id, room_id, tag, body)
+
+        yield self.notifier.on_new_event(
+            "private_user_data_key", max_id, users=[user_id]
+        )
+
+        defer.returnValue((200, {}))
+
+    @defer.inlineCallbacks
+    def on_DELETE(self, request, user_id, room_id, tag):
+        auth_user, _ = yield self.auth.get_user_by_req(request)
+        if user_id != auth_user.to_string():
+            raise AuthError(403, "Cannot add tags for other users.")
+
+        max_id = yield self.store.remove_tag_from_room(user_id, room_id, tag)
+
+        yield self.notifier.on_new_event(
+            "private_user_data_key", max_id, users=[user_id]
+        )
+
+        defer.returnValue((200, {}))
+
+
+def register_servlets(hs, http_server):
+    TagListServlet(hs).register(http_server)
+    TagServlet(hs).register(http_server)
diff --git a/synapse/storage/__init__.py b/synapse/storage/__init__.py
index a1bd9c4ce..e7443f283 100644
--- a/synapse/storage/__init__.py
+++ b/synapse/storage/__init__.py
@@ -41,6 +41,7 @@ from .end_to_end_keys import EndToEndKeyStore
 
 from .receipts import ReceiptsStore
 from .search import SearchStore
+from .tags import TagsStore
 
 
 import logging
@@ -71,6 +72,7 @@ class DataStore(RoomMemberStore, RoomStore,
                 ReceiptsStore,
                 EndToEndKeyStore,
                 SearchStore,
+                TagsStore,
                 ):
 
     def __init__(self, hs):
diff --git a/synapse/storage/schema/delta/25/tags.sql b/synapse/storage/schema/delta/25/tags.sql
new file mode 100644
index 000000000..527424c99
--- /dev/null
+++ b/synapse/storage/schema/delta/25/tags.sql
@@ -0,0 +1,38 @@
+/* Copyright 2015 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.
+ */
+
+
+CREATE TABLE IF NOT EXISTS room_tags(
+    user_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    tag     TEXT NOT NULL,  -- The name of the tag.
+    content TEXT NOT NULL,  -- The JSON content of the tag.
+    CONSTRAINT room_tag_uniqueness UNIQUE (user_id, room_id, tag)
+);
+
+CREATE TABLE IF NOT EXISTS room_tags_revisions (
+    user_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    stream_id BIGINT NOT NULL, -- The current version of the room tags.
+    CONSTRAINT room_tag_revisions_uniqueness UNIQUE (user_id, room_id)
+);
+
+CREATE TABLE IF NOT EXISTS private_user_data_max_stream_id(
+    Lock CHAR(1) NOT NULL DEFAULT 'X' UNIQUE,  -- Makes sure this table only has one row.
+    stream_id  BIGINT NOT NULL,
+    CHECK (Lock='X')
+);
+
+INSERT INTO private_user_data_max_stream_id (stream_id) VALUES (0);
diff --git a/synapse/storage/tags.py b/synapse/storage/tags.py
new file mode 100644
index 000000000..641ea250f
--- /dev/null
+++ b/synapse/storage/tags.py
@@ -0,0 +1,216 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014, 2015 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 SQLBaseStore
+from synapse.util.caches.descriptors import cached
+from twisted.internet import defer
+from .util.id_generators import StreamIdGenerator
+
+import ujson as json
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class TagsStore(SQLBaseStore):
+    def __init__(self, hs):
+        super(TagsStore, self).__init__(hs)
+
+        self._private_user_data_id_gen = StreamIdGenerator(
+            "private_user_data_max_stream_id", "stream_id"
+        )
+
+    def get_max_private_user_data_stream_id(self):
+        """Get the current max stream id for the private user data stream
+
+        Returns:
+            A deferred int.
+        """
+        return self._private_user_data_id_gen.get_max_token(self)
+
+    @cached()
+    def get_tags_for_user(self, user_id):
+        """Get all the tags for a user.
+
+
+        Args:
+            user_id(str): The user to get the tags for.
+        Returns:
+            A deferred dict mapping from room_id strings to lists of tag
+            strings.
+        """
+
+        deferred = self._simple_select_list(
+            "room_tags", {"user_id": user_id}, ["room_id", "tag", "content"]
+        )
+
+        @deferred.addCallback
+        def tags_by_room(rows):
+            tags_by_room = {}
+            for row in rows:
+                room_tags = tags_by_room.setdefault(row["room_id"], {})
+                room_tags[row["tag"]] = json.loads(row["content"])
+            return tags_by_room
+
+        return deferred
+
+    @defer.inlineCallbacks
+    def get_updated_tags(self, user_id, stream_id):
+        """Get all the tags for the rooms where the tags have changed since the
+        given version
+
+        Args:
+            user_id(str): The user to get the tags for.
+            stream_id(int): The earliest update to get for the user.
+        Returns:
+            A deferred dict mapping from room_id strings to lists of tag
+            strings for all the rooms that changed since the stream_id token.
+        """
+        def get_updated_tags_txn(txn):
+            sql = (
+                "SELECT room_id from room_tags_revisions"
+                " WHERE user_id = ? AND stream_id > ?"
+            )
+            txn.execute(sql, (user_id, stream_id))
+            room_ids = [row[0] for row in txn.fetchall()]
+            return room_ids
+
+        room_ids = yield self.runInteraction(
+            "get_updated_tags", get_updated_tags_txn
+        )
+
+        results = {}
+        if room_ids:
+            tags_by_room = yield self.get_tags_for_user(user_id)
+            for room_id in room_ids:
+                results[room_id] = tags_by_room[room_id]
+
+        defer.returnValue(results)
+
+    def get_tags_for_room(self, user_id, room_id):
+        """Get all the tags for the given room
+        Args:
+            user_id(str): The user to get tags for
+            room_id(str): The room to get tags for
+        Returns:
+            A deferred list of string tags.
+        """
+        return self._simple_select_list(
+            table="room_tags",
+            keyvalues={"user_id": user_id, "room_id": room_id},
+            retcols=("tag", "content"),
+            desc="get_tags_for_room",
+        ).addCallback(lambda rows: {
+            row["tag"]: json.loads(row["content"]) for row in rows
+        })
+
+    @defer.inlineCallbacks
+    def add_tag_to_room(self, user_id, room_id, tag, content):
+        """Add a tag to a room for a user.
+        Args:
+            user_id(str): The user to add a tag for.
+            room_id(str): The room to add a tag for.
+            tag(str): The tag name to add.
+            content(dict): A json object to associate with the tag.
+        Returns:
+            A deferred that completes once the tag has been added.
+        """
+        content_json = json.dumps(content)
+
+        def add_tag_txn(txn, next_id):
+            self._simple_upsert_txn(
+                txn,
+                table="room_tags",
+                keyvalues={
+                    "user_id": user_id,
+                    "room_id": room_id,
+                    "tag": tag,
+                },
+                values={
+                    "content": content_json,
+                }
+            )
+            self._update_revision_txn(txn, user_id, room_id, next_id)
+
+        with (yield self._private_user_data_id_gen.get_next(self)) as next_id:
+            yield self.runInteraction("add_tag", add_tag_txn, next_id)
+
+        self.get_tags_for_user.invalidate((user_id,))
+
+        result = yield self._private_user_data_id_gen.get_max_token(self)
+        defer.returnValue(result)
+
+    @defer.inlineCallbacks
+    def remove_tag_from_room(self, user_id, room_id, tag):
+        """Remove a tag from a room for a user.
+        Returns:
+            A deferred that completes once the tag has been removed
+        """
+        def remove_tag_txn(txn, next_id):
+            sql = (
+                "DELETE FROM room_tags "
+                " WHERE user_id = ? AND room_id = ? AND tag = ?"
+            )
+            txn.execute(sql, (user_id, room_id, tag))
+            self._update_revision_txn(txn, user_id, room_id, next_id)
+
+        with (yield self._private_user_data_id_gen.get_next(self)) as next_id:
+            yield self.runInteraction("remove_tag", remove_tag_txn, next_id)
+
+        self.get_tags_for_user.invalidate((user_id,))
+
+        result = yield self._private_user_data_id_gen.get_max_token(self)
+        defer.returnValue(result)
+
+    def _update_revision_txn(self, txn, user_id, room_id, next_id):
+        """Update the latest revision of the tags for the given user and room.
+
+        Args:
+            txn: The database cursor
+            user_id(str): The ID of the user.
+            room_id(str): The ID of the room.
+            next_id(int): The the revision to advance to.
+        """
+
+        update_max_id_sql = (
+            "UPDATE private_user_data_max_stream_id"
+            " SET stream_id = ?"
+            " WHERE stream_id < ?"
+        )
+        txn.execute(update_max_id_sql, (next_id, next_id))
+
+        update_sql = (
+            "UPDATE room_tags_revisions"
+            " SET stream_id = ?"
+            " WHERE user_id = ?"
+            " AND room_id = ?"
+        )
+        txn.execute(update_sql, (next_id, user_id, room_id))
+
+        if txn.rowcount == 0:
+            insert_sql = (
+                "INSERT INTO room_tags_revisions (user_id, room_id, stream_id)"
+                " VALUES (?, ?, ?)"
+            )
+            try:
+                txn.execute(insert_sql, (user_id, room_id, next_id))
+            except self.database_engine.module.IntegrityError:
+                # Ignore insertion errors. It doesn't matter if the row wasn't
+                # inserted because if two updates happend concurrently the one
+                # with the higher stream_id will not be reported to a client
+                # unless the previous update has completed. It doesn't matter
+                # which stream_id ends up in the table, as long as it is higher
+                # than the id that the client has.
+                pass
diff --git a/synapse/streams/events.py b/synapse/streams/events.py
index 699083ae1..f0d68b5bf 100644
--- a/synapse/streams/events.py
+++ b/synapse/streams/events.py
@@ -21,6 +21,7 @@ from synapse.handlers.presence import PresenceEventSource
 from synapse.handlers.room import RoomEventSource
 from synapse.handlers.typing import TypingNotificationEventSource
 from synapse.handlers.receipts import ReceiptEventSource
+from synapse.handlers.private_user_data import PrivateUserDataEventSource
 
 
 class EventSources(object):
@@ -29,6 +30,7 @@ class EventSources(object):
         "presence": PresenceEventSource,
         "typing": TypingNotificationEventSource,
         "receipt": ReceiptEventSource,
+        "private_user_data": PrivateUserDataEventSource,
     }
 
     def __init__(self, hs):
@@ -52,5 +54,8 @@ class EventSources(object):
             receipt_key=(
                 yield self.sources["receipt"].get_current_key()
             ),
+            private_user_data_key=(
+                yield self.sources["private_user_data"].get_current_key()
+            ),
         )
         defer.returnValue(token)
diff --git a/synapse/types.py b/synapse/types.py
index 8c51e00e8..28344d8b3 100644
--- a/synapse/types.py
+++ b/synapse/types.py
@@ -98,10 +98,13 @@ class EventID(DomainSpecificString):
 
 
 class StreamToken(
-    namedtuple(
-        "Token",
-        ("room_key", "presence_key", "typing_key", "receipt_key")
-    )
+    namedtuple("Token", (
+        "room_key",
+        "presence_key",
+        "typing_key",
+        "receipt_key",
+        "private_user_data_key",
+    ))
 ):
     _SEPARATOR = "_"
 
@@ -109,7 +112,7 @@ class StreamToken(
     def from_string(cls, string):
         try:
             keys = string.split(cls._SEPARATOR)
-            if len(keys) == len(cls._fields) - 1:
+            while len(keys) < len(cls._fields):
                 # i.e. old token from before receipt_key
                 keys.append("0")
             return cls(*keys)
@@ -128,13 +131,14 @@ class StreamToken(
         else:
             return int(self.room_key[1:].split("-")[-1])
 
-    def is_after(self, other_token):
+    def is_after(self, other):
         """Does this token contain events that the other doesn't?"""
         return (
-            (other_token.room_stream_id < self.room_stream_id)
-            or (int(other_token.presence_key) < int(self.presence_key))
-            or (int(other_token.typing_key) < int(self.typing_key))
-            or (int(other_token.receipt_key) < int(self.receipt_key))
+            (other.room_stream_id < self.room_stream_id)
+            or (int(other.presence_key) < int(self.presence_key))
+            or (int(other.typing_key) < int(self.typing_key))
+            or (int(other.receipt_key) < int(self.receipt_key))
+            or (int(other.private_user_data_key) < int(self.private_user_data_key))
         )
 
     def copy_and_advance(self, key, new_value):
diff --git a/tests/rest/client/v1/test_presence.py b/tests/rest/client/v1/test_presence.py
index 29d9bbaad..0e3b92224 100644
--- a/tests/rest/client/v1/test_presence.py
+++ b/tests/rest/client/v1/test_presence.py
@@ -369,7 +369,7 @@ class PresenceEventStreamTestCase(unittest.TestCase):
         # all be ours
 
         # I'll already get my own presence state change
-        self.assertEquals({"start": "0_1_0_0", "end": "0_1_0_0", "chunk": []},
+        self.assertEquals({"start": "0_1_0_0_0", "end": "0_1_0_0_0", "chunk": []},
             response
         )
 
@@ -388,7 +388,7 @@ class PresenceEventStreamTestCase(unittest.TestCase):
                 "/events?from=s0_1_0&timeout=0", None)
 
         self.assertEquals(200, code)
-        self.assertEquals({"start": "s0_1_0_0", "end": "s0_2_0_0", "chunk": [
+        self.assertEquals({"start": "s0_1_0_0_0", "end": "s0_2_0_0_0", "chunk": [
             {"type": "m.presence",
              "content": {
                  "user_id": "@banana:test",