diff --git a/changelog.d/11483.misc b/changelog.d/11483.misc
new file mode 100644
index 0000000000..4cc47fcab9
--- /dev/null
+++ b/changelog.d/11483.misc
@@ -0,0 +1 @@
+Add missing type hints to `synapse.federation`.
diff --git a/mypy.ini b/mypy.ini
index 99b5c41ad6..d8296b4fa3 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -158,6 +158,12 @@ disallow_untyped_defs = True
 [mypy-synapse.events.*]
 disallow_untyped_defs = True
 
+[mypy-synapse.federation.*]
+disallow_untyped_defs = True
+
+[mypy-synapse.federation.transport.client]
+disallow_untyped_defs = False
+
 [mypy-synapse.handlers.*]
 disallow_untyped_defs = True
 
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index be1423da24..fee1477ab6 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -128,7 +128,7 @@ class FederationClient(FederationBase):
             reset_expiry_on_get=False,
         )
 
-    def _clear_tried_cache(self):
+    def _clear_tried_cache(self) -> None:
         """Clear pdu_destination_tried cache"""
         now = self._clock.time_msec()
 
@@ -800,7 +800,7 @@ class FederationClient(FederationBase):
                 no servers successfully handle the request.
         """
 
-        async def send_request(destination) -> SendJoinResult:
+        async def send_request(destination: str) -> SendJoinResult:
             response = await self._do_send_join(room_version, destination, pdu)
 
             # If an event was returned (and expected to be returned):
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index cce85526e7..8e37e76206 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -1,6 +1,6 @@
 # Copyright 2015, 2016 OpenMarket Ltd
 # Copyright 2018 New Vector Ltd
-# Copyright 2019 Matrix.org Federation C.I.C
+# Copyright 2019-2021 Matrix.org Federation 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.
@@ -450,7 +450,7 @@ class FederationServer(FederationBase):
         # require callouts to other servers to fetch missing events), but
         # impose a limit to avoid going too crazy with ram/cpu.
 
-        async def process_pdus_for_room(room_id: str):
+        async def process_pdus_for_room(room_id: str) -> None:
             with nested_logging_context(room_id):
                 logger.debug("Processing PDUs for %s", room_id)
 
@@ -547,7 +547,7 @@ class FederationServer(FederationBase):
 
     async def on_state_ids_request(
         self, origin: str, room_id: str, event_id: str
-    ) -> Tuple[int, Dict[str, Any]]:
+    ) -> Tuple[int, JsonDict]:
         if not event_id:
             raise NotImplementedError("Specify an event")
 
@@ -567,7 +567,9 @@ class FederationServer(FederationBase):
 
         return 200, resp
 
-    async def _on_state_ids_request_compute(self, room_id, event_id):
+    async def _on_state_ids_request_compute(
+        self, room_id: str, event_id: str
+    ) -> JsonDict:
         state_ids = await self.handler.get_state_ids_for_pdu(room_id, event_id)
         auth_chain_ids = await self.store.get_auth_chain_ids(room_id, state_ids)
         return {"pdu_ids": state_ids, "auth_chain_ids": auth_chain_ids}
diff --git a/synapse/federation/persistence.py b/synapse/federation/persistence.py
index 4fead6ca29..523ab1c51e 100644
--- a/synapse/federation/persistence.py
+++ b/synapse/federation/persistence.py
@@ -1,4 +1,5 @@
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2021 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.
@@ -23,6 +24,7 @@ from typing import Optional, Tuple
 
 from synapse.federation.units import Transaction
 from synapse.logging.utils import log_function
+from synapse.storage.databases.main import DataStore
 from synapse.types import JsonDict
 
 logger = logging.getLogger(__name__)
@@ -31,7 +33,7 @@ logger = logging.getLogger(__name__)
 class TransactionActions:
     """Defines persistence actions that relate to handling Transactions."""
 
-    def __init__(self, datastore):
+    def __init__(self, datastore: DataStore):
         self.store = datastore
 
     @log_function
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index 1fbf325fdc..63289a5a33 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -1,4 +1,5 @@
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2021 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.
@@ -350,7 +351,7 @@ class BaseFederationRow:
     TypeId = ""  # Unique string that ids the type. Must be overridden in sub classes.
 
     @staticmethod
-    def from_data(data):
+    def from_data(data: JsonDict) -> "BaseFederationRow":
         """Parse the data from the federation stream into a row.
 
         Args:
@@ -359,7 +360,7 @@ class BaseFederationRow:
         """
         raise NotImplementedError()
 
-    def to_data(self):
+    def to_data(self) -> JsonDict:
         """Serialize this row to be sent over the federation stream.
 
         Returns:
@@ -368,7 +369,7 @@ class BaseFederationRow:
         """
         raise NotImplementedError()
 
-    def add_to_buffer(self, buff):
+    def add_to_buffer(self, buff: "ParsedFederationStreamData") -> None:
         """Add this row to the appropriate field in the buffer ready for this
         to be sent over federation.
 
@@ -391,15 +392,15 @@ class PresenceDestinationsRow(
     TypeId = "pd"
 
     @staticmethod
-    def from_data(data):
+    def from_data(data: JsonDict) -> "PresenceDestinationsRow":
         return PresenceDestinationsRow(
             state=UserPresenceState.from_dict(data["state"]), destinations=data["dests"]
         )
 
-    def to_data(self):
+    def to_data(self) -> JsonDict:
         return {"state": self.state.as_dict(), "dests": self.destinations}
 
-    def add_to_buffer(self, buff):
+    def add_to_buffer(self, buff: "ParsedFederationStreamData") -> None:
         buff.presence_destinations.append((self.state, self.destinations))
 
 
@@ -417,13 +418,13 @@ class KeyedEduRow(
     TypeId = "k"
 
     @staticmethod
-    def from_data(data):
+    def from_data(data: JsonDict) -> "KeyedEduRow":
         return KeyedEduRow(key=tuple(data["key"]), edu=Edu(**data["edu"]))
 
-    def to_data(self):
+    def to_data(self) -> JsonDict:
         return {"key": self.key, "edu": self.edu.get_internal_dict()}
 
-    def add_to_buffer(self, buff):
+    def add_to_buffer(self, buff: "ParsedFederationStreamData") -> None:
         buff.keyed_edus.setdefault(self.edu.destination, {})[self.key] = self.edu
 
 
@@ -433,13 +434,13 @@ class EduRow(BaseFederationRow, namedtuple("EduRow", ("edu",))):  # Edu
     TypeId = "e"
 
     @staticmethod
-    def from_data(data):
+    def from_data(data: JsonDict) -> "EduRow":
         return EduRow(Edu(**data))
 
-    def to_data(self):
+    def to_data(self) -> JsonDict:
         return self.edu.get_internal_dict()
 
-    def add_to_buffer(self, buff):
+    def add_to_buffer(self, buff: "ParsedFederationStreamData") -> None:
         buff.edus.setdefault(self.edu.destination, []).append(self.edu)
 
 
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index afe35e72b6..391b30fbb5 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -1,5 +1,6 @@
 # Copyright 2014-2016 OpenMarket Ltd
 # Copyright 2019 New Vector Ltd
+# Copyright 2021 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.
@@ -14,7 +15,8 @@
 # limitations under the License.
 import datetime
 import logging
-from typing import TYPE_CHECKING, Dict, Hashable, Iterable, List, Optional, Tuple
+from types import TracebackType
+from typing import TYPE_CHECKING, Dict, Hashable, Iterable, List, Optional, Tuple, Type
 
 import attr
 from prometheus_client import Counter
@@ -213,7 +215,7 @@ class PerDestinationQueue:
         self._pending_edus_keyed[(edu.edu_type, key)] = edu
         self.attempt_new_transaction()
 
-    def send_edu(self, edu) -> None:
+    def send_edu(self, edu: Edu) -> None:
         self._pending_edus.append(edu)
         self.attempt_new_transaction()
 
@@ -701,7 +703,12 @@ class _TransactionQueueManager:
 
         return self._pdus, pending_edus
 
-    async def __aexit__(self, exc_type, exc, tb):
+    async def __aexit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc: Optional[BaseException],
+        tb: Optional[TracebackType],
+    ) -> None:
         if exc_type is not None:
             # Failed to send transaction, so we bail out.
             return
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index d1f4be641d..9fc4c31c93 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -21,6 +21,7 @@ from typing import (
     Callable,
     Collection,
     Dict,
+    Generator,
     Iterable,
     List,
     Mapping,
@@ -235,11 +236,16 @@ class TransportLayerClient:
 
     @log_function
     async def make_query(
-        self, destination, query_type, args, retry_on_dns_fail, ignore_backoff=False
-    ):
+        self,
+        destination: str,
+        query_type: str,
+        args: dict,
+        retry_on_dns_fail: bool,
+        ignore_backoff: bool = False,
+    ) -> JsonDict:
         path = _create_v1_path("/query/%s", query_type)
 
-        content = await self.client.get_json(
+        return await self.client.get_json(
             destination=destination,
             path=path,
             args=args,
@@ -248,8 +254,6 @@ class TransportLayerClient:
             ignore_backoff=ignore_backoff,
         )
 
-        return content
-
     @log_function
     async def make_membership_event(
         self,
@@ -1317,7 +1321,7 @@ class SendJoinResponse:
 
 
 @ijson.coroutine
-def _event_parser(event_dict: JsonDict):
+def _event_parser(event_dict: JsonDict) -> Generator[None, Tuple[str, Any], None]:
     """Helper function for use with `ijson.kvitems_coro` to parse key-value pairs
     to add them to a given dictionary.
     """
@@ -1328,7 +1332,9 @@ def _event_parser(event_dict: JsonDict):
 
 
 @ijson.coroutine
-def _event_list_parser(room_version: RoomVersion, events: List[EventBase]):
+def _event_list_parser(
+    room_version: RoomVersion, events: List[EventBase]
+) -> Generator[None, JsonDict, None]:
     """Helper function for use with `ijson.items_coro` to parse an array of
     events and add them to the given list.
     """
diff --git a/synapse/federation/transport/server/__init__.py b/synapse/federation/transport/server/__init__.py
index abcb8728f5..77b936361a 100644
--- a/synapse/federation/transport/server/__init__.py
+++ b/synapse/federation/transport/server/__init__.py
@@ -302,7 +302,7 @@ def register_servlets(
     authenticator: Authenticator,
     ratelimiter: FederationRateLimiter,
     servlet_groups: Optional[Iterable[str]] = None,
-):
+) -> None:
     """Initialize and register servlet classes.
 
     Will by default register all servlets. For custom behaviour, pass in
diff --git a/synapse/federation/transport/server/_base.py b/synapse/federation/transport/server/_base.py
index cef65929c5..dc39e3537b 100644
--- a/synapse/federation/transport/server/_base.py
+++ b/synapse/federation/transport/server/_base.py
@@ -15,10 +15,13 @@
 import functools
 import logging
 import re
+from typing import Any, Awaitable, Callable, Optional, Tuple, cast
 
 from synapse.api.errors import Codes, FederationDeniedError, SynapseError
 from synapse.api.urls import FEDERATION_V1_PREFIX
+from synapse.http.server import HttpServer, ServletCallback
 from synapse.http.servlet import parse_json_object_from_request
+from synapse.http.site import SynapseRequest
 from synapse.logging import opentracing
 from synapse.logging.context import run_in_background
 from synapse.logging.opentracing import (
@@ -29,6 +32,7 @@ from synapse.logging.opentracing import (
     whitelisted_homeserver,
 )
 from synapse.server import HomeServer
+from synapse.types import JsonDict
 from synapse.util.ratelimitutils import FederationRateLimiter
 from synapse.util.stringutils import parse_and_validate_server_name
 
@@ -59,9 +63,11 @@ class Authenticator:
             self.replication_client = hs.get_tcp_replication()
 
     # A method just so we can pass 'self' as the authenticator to the Servlets
-    async def authenticate_request(self, request, content):
+    async def authenticate_request(
+        self, request: SynapseRequest, content: Optional[JsonDict]
+    ) -> str:
         now = self._clock.time_msec()
-        json_request = {
+        json_request: JsonDict = {
             "method": request.method.decode("ascii"),
             "uri": request.uri.decode("ascii"),
             "destination": self.server_name,
@@ -114,7 +120,7 @@ class Authenticator:
 
         return origin
 
-    async def _reset_retry_timings(self, origin):
+    async def _reset_retry_timings(self, origin: str) -> None:
         try:
             logger.info("Marking origin %r as up", origin)
             await self.store.set_destination_retry_timings(origin, None, 0, 0)
@@ -133,14 +139,14 @@ class Authenticator:
             logger.exception("Error resetting retry timings on %s", origin)
 
 
-def _parse_auth_header(header_bytes):
+def _parse_auth_header(header_bytes: bytes) -> Tuple[str, str, str]:
     """Parse an X-Matrix auth header
 
     Args:
-        header_bytes (bytes): header value
+        header_bytes: header value
 
     Returns:
-        Tuple[str, str, str]: origin, key id, signature.
+        origin, key id, signature.
 
     Raises:
         AuthenticationError if the header could not be parsed
@@ -148,9 +154,9 @@ def _parse_auth_header(header_bytes):
     try:
         header_str = header_bytes.decode("utf-8")
         params = header_str.split(" ")[1].split(",")
-        param_dict = dict(kv.split("=") for kv in params)
+        param_dict = {k: v for k, v in (kv.split("=", maxsplit=1) for kv in params)}
 
-        def strip_quotes(value):
+        def strip_quotes(value: str) -> str:
             if value.startswith('"'):
                 return value[1:-1]
             else:
@@ -233,23 +239,25 @@ class BaseFederationServlet:
         self.ratelimiter = ratelimiter
         self.server_name = server_name
 
-    def _wrap(self, func):
+    def _wrap(self, func: Callable[..., Awaitable[Tuple[int, Any]]]) -> ServletCallback:
         authenticator = self.authenticator
         ratelimiter = self.ratelimiter
 
         @functools.wraps(func)
-        async def new_func(request, *args, **kwargs):
+        async def new_func(
+            request: SynapseRequest, *args: Any, **kwargs: str
+        ) -> Optional[Tuple[int, Any]]:
             """A callback which can be passed to HttpServer.RegisterPaths
 
             Args:
-                request (twisted.web.http.Request):
+                request:
                 *args: unused?
-                **kwargs (dict[unicode, unicode]): the dict mapping keys to path
-                    components as specified in the path match regexp.
+                **kwargs: the dict mapping keys to path components as specified
+                    in the path match regexp.
 
             Returns:
-                Tuple[int, object]|None: (response code, response object) as returned by
-                    the callback method. None if the request has already been handled.
+                (response code, response object) as returned by the callback method.
+                None if the request has already been handled.
             """
             content = None
             if request.method in [b"PUT", b"POST"]:
@@ -257,7 +265,9 @@ class BaseFederationServlet:
                 content = parse_json_object_from_request(request)
 
             try:
-                origin = await authenticator.authenticate_request(request, content)
+                origin: Optional[str] = await authenticator.authenticate_request(
+                    request, content
+                )
             except NoAuthenticationError:
                 origin = None
                 if self.REQUIRE_AUTH:
@@ -301,7 +311,7 @@ class BaseFederationServlet:
                                 "client disconnected before we started processing "
                                 "request"
                             )
-                            return -1, None
+                            return None
                         response = await func(
                             origin, content, request.args, *args, **kwargs
                         )
@@ -312,9 +322,9 @@ class BaseFederationServlet:
 
             return response
 
-        return new_func
+        return cast(ServletCallback, new_func)
 
-    def register(self, server):
+    def register(self, server: HttpServer) -> None:
         pattern = re.compile("^" + self.PREFIX + self.PATH + "$")
 
         for method in ("GET", "PUT", "POST"):