diff --git a/changelog.d/5589.feature b/changelog.d/5589.feature
new file mode 100644
index 0000000000..a87e669dd4
--- /dev/null
+++ b/changelog.d/5589.feature
@@ -0,0 +1 @@
+Add ability to pull all locally stored events out of synapse that a particular user can see.
diff --git a/synapse/handlers/admin.py b/synapse/handlers/admin.py
index 941ebfa107..e8a651e231 100644
--- a/synapse/handlers/admin.py
+++ b/synapse/handlers/admin.py
@@ -17,6 +17,10 @@ import logging
 
 from twisted.internet import defer
 
+from synapse.api.constants import Membership
+from synapse.types import RoomStreamToken
+from synapse.visibility import filter_events_for_client
+
 from ._base import BaseHandler
 
 logger = logging.getLogger(__name__)
@@ -89,3 +93,182 @@ class AdminHandler(BaseHandler):
         ret = yield self.store.search_users(term)
 
         defer.returnValue(ret)
+
+    @defer.inlineCallbacks
+    def export_user_data(self, user_id, writer):
+        """Write all data we have on the user to the given writer.
+
+        Args:
+            user_id (str)
+            writer (ExfiltrationWriter)
+
+        Returns:
+            defer.Deferred: Resolves when all data for a user has been written.
+            The returned value is that returned by `writer.finished()`.
+        """
+        # Get all rooms the user is in or has been in
+        rooms = yield self.store.get_rooms_for_user_where_membership_is(
+            user_id,
+            membership_list=(
+                Membership.JOIN,
+                Membership.LEAVE,
+                Membership.BAN,
+                Membership.INVITE,
+            ),
+        )
+
+        # We only try and fetch events for rooms the user has been in. If
+        # they've been e.g. invited to a room without joining then we handle
+        # those seperately.
+        rooms_user_has_been_in = yield self.store.get_rooms_user_has_been_in(user_id)
+
+        for index, room in enumerate(rooms):
+            room_id = room.room_id
+
+            logger.info(
+                "[%s] Handling room %s, %d/%d", user_id, room_id, index + 1, len(rooms)
+            )
+
+            forgotten = yield self.store.did_forget(user_id, room_id)
+            if forgotten:
+                logger.info("[%s] User forgot room %d, ignoring", user_id, room_id)
+                continue
+
+            if room_id not in rooms_user_has_been_in:
+                # If we haven't been in the rooms then the filtering code below
+                # won't return anything, so we need to handle these cases
+                # explicitly.
+
+                if room.membership == Membership.INVITE:
+                    event_id = room.event_id
+                    invite = yield self.store.get_event(event_id, allow_none=True)
+                    if invite:
+                        invited_state = invite.unsigned["invite_room_state"]
+                        writer.write_invite(room_id, invite, invited_state)
+
+                continue
+
+            # We only want to bother fetching events up to the last time they
+            # were joined. We estimate that point by looking at the
+            # stream_ordering of the last membership if it wasn't a join.
+            if room.membership == Membership.JOIN:
+                stream_ordering = yield self.store.get_room_max_stream_ordering()
+            else:
+                stream_ordering = room.stream_ordering
+
+            from_key = str(RoomStreamToken(0, 0))
+            to_key = str(RoomStreamToken(None, stream_ordering))
+
+            written_events = set()  # Events that we've processed in this room
+
+            # We need to track gaps in the events stream so that we can then
+            # write out the state at those events. We do this by keeping track
+            # of events whose prev events we haven't seen.
+
+            # Map from event ID to prev events that haven't been processed,
+            # dict[str, set[str]].
+            event_to_unseen_prevs = {}
+
+            # The reverse mapping to above, i.e. map from unseen event to events
+            # that have the unseen event in their prev_events, i.e. the unseen
+            # events "children". dict[str, set[str]]
+            unseen_to_child_events = {}
+
+            # We fetch events in the room the user could see by fetching *all*
+            # events that we have and then filtering, this isn't the most
+            # efficient method perhaps but it does guarantee we get everything.
+            while True:
+                events, _ = yield self.store.paginate_room_events(
+                    room_id, from_key, to_key, limit=100, direction="f"
+                )
+                if not events:
+                    break
+
+                from_key = events[-1].internal_metadata.after
+
+                events = yield filter_events_for_client(self.store, user_id, events)
+
+                writer.write_events(room_id, events)
+
+                # Update the extremity tracking dicts
+                for event in events:
+                    # Check if we have any prev events that haven't been
+                    # processed yet, and add those to the appropriate dicts.
+                    unseen_events = set(event.prev_event_ids()) - written_events
+                    if unseen_events:
+                        event_to_unseen_prevs[event.event_id] = unseen_events
+                        for unseen in unseen_events:
+                            unseen_to_child_events.setdefault(unseen, set()).add(
+                                event.event_id
+                            )
+
+                    # Now check if this event is an unseen prev event, if so
+                    # then we remove this event from the appropriate dicts.
+                    for child_id in unseen_to_child_events.pop(event.event_id, []):
+                        event_to_unseen_prevs[child_id].discard(event.event_id)
+
+                    written_events.add(event.event_id)
+
+                logger.info(
+                    "Written %d events in room %s", len(written_events), room_id
+                )
+
+            # Extremities are the events who have at least one unseen prev event.
+            extremities = (
+                event_id
+                for event_id, unseen_prevs in event_to_unseen_prevs.items()
+                if unseen_prevs
+            )
+            for event_id in extremities:
+                if not event_to_unseen_prevs[event_id]:
+                    continue
+                state = yield self.store.get_state_for_event(event_id)
+                writer.write_state(room_id, event_id, state)
+
+        defer.returnValue(writer.finished())
+
+
+class ExfiltrationWriter(object):
+    """Interface used to specify how to write exported data.
+    """
+
+    def write_events(self, room_id, events):
+        """Write a batch of events for a room.
+
+        Args:
+            room_id (str)
+            events (list[FrozenEvent])
+        """
+        pass
+
+    def write_state(self, room_id, event_id, state):
+        """Write the state at the given event in the room.
+
+        This only gets called for backward extremities rather than for each
+        event.
+
+        Args:
+            room_id (str)
+            event_id (str)
+            state (dict[tuple[str, str], FrozenEvent])
+        """
+        pass
+
+    def write_invite(self, room_id, event, state):
+        """Write an invite for the room, with associated invite state.
+
+        Args:
+            room_id (str)
+            event (FrozenEvent)
+            state (dict[tuple[str, str], dict]): A subset of the state at the
+                invite, with a subset of the event keys (type, state_key
+                content and sender)
+        """
+
+    def finished(self):
+        """Called when all data has succesfully been exported and written.
+
+        This functions return value is passed to the caller of
+        `export_user_data`.
+        """
+        pass
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 8004aeb909..32cfd010a5 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -575,6 +575,26 @@ class RoomMemberWorkerStore(EventsWorkerStore):
         count = yield self.runInteraction("did_forget_membership", f)
         defer.returnValue(count == 0)
 
+    @defer.inlineCallbacks
+    def get_rooms_user_has_been_in(self, user_id):
+        """Get all rooms that the user has ever been in.
+
+        Args:
+            user_id (str)
+
+        Returns:
+            Deferred[set[str]]: Set of room IDs.
+        """
+
+        room_ids = yield self._simple_select_onecol(
+            table="room_memberships",
+            keyvalues={"membership": Membership.JOIN, "user_id": user_id},
+            retcol="room_id",
+            desc="get_rooms_user_has_been_in",
+        )
+
+        return set(room_ids)
+
 
 class RoomMemberStore(RoomMemberWorkerStore):
     def __init__(self, db_conn, hs):
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index 386a9dbe14..a0465484df 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -833,7 +833,9 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
         Returns:
             Deferred[tuple[list[_EventDictReturn], str]]: Returns the results
             as a list of _EventDictReturn and a token that points to the end
-            of the result set.
+            of the result set. If no events are returned then the end of the
+            stream has been reached (i.e. there are no events between
+            `from_token` and `to_token`), or `limit` is zero.
         """
 
         assert int(limit) >= 0
@@ -905,15 +907,15 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                 only those before
             direction(char): Either 'b' or 'f' to indicate whether we are
                 paginating forwards or backwards from `from_key`.
-            limit (int): The maximum number of events to return. Zero or less
-                means no limit.
+            limit (int): The maximum number of events to return.
             event_filter (Filter|None): If provided filters the events to
                 those that match the filter.
 
         Returns:
-            tuple[list[dict], str]: Returns the results as a list of dicts and
-            a token that points to the end of the result set. The dicts have
-            the keys "event_id", "topological_ordering" and "stream_orderign".
+            tuple[list[FrozenEvent], str]: Returns the results as a list of
+            events and a token that points to the end of the result set. If no
+            events are returned then the end of the stream has been reached
+            (i.e. there are no events between `from_key` and `to_key`).
         """
 
         from_key = RoomStreamToken.parse(from_key)
diff --git a/tests/handlers/test_admin.py b/tests/handlers/test_admin.py
new file mode 100644
index 0000000000..fc37c4328c
--- /dev/null
+++ b/tests/handlers/test_admin.py
@@ -0,0 +1,210 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# 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 collections import Counter
+
+from mock import Mock
+
+import synapse.api.errors
+import synapse.handlers.admin
+import synapse.rest.admin
+import synapse.storage
+from synapse.api.constants import EventTypes
+from synapse.rest.client.v1 import login, room
+
+from tests import unittest
+
+
+class ExfiltrateData(unittest.HomeserverTestCase):
+    servlets = [
+        synapse.rest.admin.register_servlets_for_client_rest_resource,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def prepare(self, reactor, clock, hs):
+        self.admin_handler = hs.get_handlers().admin_handler
+
+        self.user1 = self.register_user("user1", "password")
+        self.token1 = self.login("user1", "password")
+
+        self.user2 = self.register_user("user2", "password")
+        self.token2 = self.login("user2", "password")
+
+    def test_single_public_joined_room(self):
+        """Test that we write *all* events for a public room
+        """
+        room_id = self.helper.create_room_as(
+            self.user1, tok=self.token1, is_public=True
+        )
+        self.helper.send(room_id, body="Hello!", tok=self.token1)
+        self.helper.join(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Hello again!", tok=self.token1)
+
+        writer = Mock()
+
+        self.get_success(self.admin_handler.export_user_data(self.user2, writer))
+
+        writer.write_events.assert_called()
+
+        # Since we can see all events there shouldn't be any extremities, so no
+        # state should be written
+        writer.write_state.assert_not_called()
+
+        # Collect all events that were written
+        written_events = []
+        for (called_room_id, events), _ in writer.write_events.call_args_list:
+            self.assertEqual(called_room_id, room_id)
+            written_events.extend(events)
+
+        # Check that the right number of events were written
+        counter = Counter(
+            (event.type, getattr(event, "state_key", None)) for event in written_events
+        )
+        self.assertEqual(counter[(EventTypes.Message, None)], 2)
+        self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
+        self.assertEqual(counter[(EventTypes.Member, self.user2)], 1)
+
+    def test_single_private_joined_room(self):
+        """Tests that we correctly write state when we can't see all events in
+        a room.
+        """
+        room_id = self.helper.create_room_as(self.user1, tok=self.token1)
+        self.helper.send_state(
+            room_id,
+            EventTypes.RoomHistoryVisibility,
+            body={"history_visibility": "joined"},
+            tok=self.token1,
+        )
+        self.helper.send(room_id, body="Hello!", tok=self.token1)
+        self.helper.join(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Hello again!", tok=self.token1)
+
+        writer = Mock()
+
+        self.get_success(self.admin_handler.export_user_data(self.user2, writer))
+
+        writer.write_events.assert_called()
+
+        # Since we can't see all events there should be one extremity.
+        writer.write_state.assert_called_once()
+
+        # Collect all events that were written
+        written_events = []
+        for (called_room_id, events), _ in writer.write_events.call_args_list:
+            self.assertEqual(called_room_id, room_id)
+            written_events.extend(events)
+
+        # Check that the right number of events were written
+        counter = Counter(
+            (event.type, getattr(event, "state_key", None)) for event in written_events
+        )
+        self.assertEqual(counter[(EventTypes.Message, None)], 1)
+        self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
+        self.assertEqual(counter[(EventTypes.Member, self.user2)], 1)
+
+    def test_single_left_room(self):
+        """Tests that we don't see events in the room after we leave.
+        """
+        room_id = self.helper.create_room_as(self.user1, tok=self.token1)
+        self.helper.send(room_id, body="Hello!", tok=self.token1)
+        self.helper.join(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Hello again!", tok=self.token1)
+        self.helper.leave(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Helloooooo!", tok=self.token1)
+
+        writer = Mock()
+
+        self.get_success(self.admin_handler.export_user_data(self.user2, writer))
+
+        writer.write_events.assert_called()
+
+        # Since we can see all events there shouldn't be any extremities, so no
+        # state should be written
+        writer.write_state.assert_not_called()
+
+        written_events = []
+        for (called_room_id, events), _ in writer.write_events.call_args_list:
+            self.assertEqual(called_room_id, room_id)
+            written_events.extend(events)
+
+        # Check that the right number of events were written
+        counter = Counter(
+            (event.type, getattr(event, "state_key", None)) for event in written_events
+        )
+        self.assertEqual(counter[(EventTypes.Message, None)], 2)
+        self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
+        self.assertEqual(counter[(EventTypes.Member, self.user2)], 2)
+
+    def test_single_left_rejoined_private_room(self):
+        """Tests that see the correct events in private rooms when we
+        repeatedly join and leave.
+        """
+        room_id = self.helper.create_room_as(self.user1, tok=self.token1)
+        self.helper.send_state(
+            room_id,
+            EventTypes.RoomHistoryVisibility,
+            body={"history_visibility": "joined"},
+            tok=self.token1,
+        )
+        self.helper.send(room_id, body="Hello!", tok=self.token1)
+        self.helper.join(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Hello again!", tok=self.token1)
+        self.helper.leave(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Helloooooo!", tok=self.token1)
+        self.helper.join(room_id, self.user2, tok=self.token2)
+        self.helper.send(room_id, body="Helloooooo!!", tok=self.token1)
+
+        writer = Mock()
+
+        self.get_success(self.admin_handler.export_user_data(self.user2, writer))
+
+        writer.write_events.assert_called_once()
+
+        # Since we joined/left/joined again we expect there to be two gaps.
+        self.assertEqual(writer.write_state.call_count, 2)
+
+        written_events = []
+        for (called_room_id, events), _ in writer.write_events.call_args_list:
+            self.assertEqual(called_room_id, room_id)
+            written_events.extend(events)
+
+        # Check that the right number of events were written
+        counter = Counter(
+            (event.type, getattr(event, "state_key", None)) for event in written_events
+        )
+        self.assertEqual(counter[(EventTypes.Message, None)], 2)
+        self.assertEqual(counter[(EventTypes.Member, self.user1)], 1)
+        self.assertEqual(counter[(EventTypes.Member, self.user2)], 3)
+
+    def test_invite(self):
+        """Tests that pending invites get handled correctly.
+        """
+        room_id = self.helper.create_room_as(self.user1, tok=self.token1)
+        self.helper.send(room_id, body="Hello!", tok=self.token1)
+        self.helper.invite(room_id, self.user1, self.user2, tok=self.token1)
+
+        writer = Mock()
+
+        self.get_success(self.admin_handler.export_user_data(self.user2, writer))
+
+        writer.write_events.assert_not_called()
+        writer.write_state.assert_not_called()
+        writer.write_invite.assert_called_once()
+
+        args = writer.write_invite.call_args[0]
+        self.assertEqual(args[0], room_id)
+        self.assertEqual(args[1].content["membership"], "invite")
+        self.assertTrue(args[2])  # Assert there is at least one bit of state
diff --git a/tests/unittest.py b/tests/unittest.py
index 0f0c2ad69d..cabe787cb4 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -472,7 +472,7 @@ class HomeserverTestCase(TestCase):
             "POST", "/_matrix/client/r0/admin/register", body.encode("utf8")
         )
         self.render(request)
-        self.assertEqual(channel.code, 200)
+        self.assertEqual(channel.code, 200, channel.json_body)
 
         user_id = channel.json_body["user_id"]
         return user_id