diff --git a/changelog.d/9442.misc b/changelog.d/9442.misc
new file mode 100644
index 000000000..e7f0b6262
--- /dev/null
+++ b/changelog.d/9442.misc
@@ -0,0 +1 @@
+Add type hints to the caching module.
diff --git a/synapse/http/federation/well_known_resolver.py b/synapse/http/federation/well_known_resolver.py
index ecd63e659..ce4079f15 100644
--- a/synapse/http/federation/well_known_resolver.py
+++ b/synapse/http/federation/well_known_resolver.py
@@ -71,8 +71,10 @@ WELL_KNOWN_RETRY_ATTEMPTS = 3
 logger = logging.getLogger(__name__)
 
 
-_well_known_cache = TTLCache("well-known")
-_had_valid_well_known_cache = TTLCache("had-valid-well-known")
+_well_known_cache = TTLCache("well-known")  # type: TTLCache[bytes, Optional[bytes]]
+_had_valid_well_known_cache = TTLCache(
+    "had-valid-well-known"
+)  # type: TTLCache[bytes, bool]
 
 
 @attr.s(slots=True, frozen=True)
@@ -88,8 +90,8 @@ class WellKnownResolver:
         reactor: IReactorTime,
         agent: IAgent,
         user_agent: bytes,
-        well_known_cache: Optional[TTLCache] = None,
-        had_well_known_cache: Optional[TTLCache] = None,
+        well_known_cache: Optional[TTLCache[bytes, Optional[bytes]]] = None,
+        had_well_known_cache: Optional[TTLCache[bytes, bool]] = None,
     ):
         self._reactor = reactor
         self._clock = Clock(reactor)
diff --git a/synapse/storage/databases/state/store.py b/synapse/storage/databases/state/store.py
index e2240703a..97ec65f75 100644
--- a/synapse/storage/databases/state/store.py
+++ b/synapse/storage/databases/state/store.py
@@ -183,12 +183,13 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
         requests state from the cache, if False we need to query the DB for the
         missing state.
         """
-        is_all, known_absent, state_dict_ids = cache.get(group)
+        cache_entry = cache.get(group)
+        state_dict_ids = cache_entry.value
 
-        if is_all or state_filter.is_full():
+        if cache_entry.full or state_filter.is_full():
             # Either we have everything or want everything, either way
             # `is_all` tells us whether we've gotten everything.
-            return state_filter.filter_state(state_dict_ids), is_all
+            return state_filter.filter_state(state_dict_ids), cache_entry.full
 
         # tracks whether any of our requested types are missing from the cache
         missing_types = False
@@ -202,7 +203,7 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
             # There aren't any wild cards, so `concrete_types()` returns the
             # complete list of event types we're wanting.
             for key in state_filter.concrete_types():
-                if key not in state_dict_ids and key not in known_absent:
+                if key not in state_dict_ids and key not in cache_entry.known_absent:
                     missing_types = True
                     break
 
diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index 588d2d49f..b3b413b02 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/synapse/util/caches/dictionary_cache.py
@@ -15,26 +15,38 @@
 import enum
 import logging
 import threading
-from collections import namedtuple
-from typing import Any
+from typing import Any, Dict, Generic, Iterable, Optional, Set, TypeVar
+
+import attr
 
 from synapse.util.caches.lrucache import LruCache
 
 logger = logging.getLogger(__name__)
 
 
-class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
+# The type of the cache keys.
+KT = TypeVar("KT")
+# The type of the dictionary keys.
+DKT = TypeVar("DKT")
+
+
+@attr.s(slots=True)
+class DictionaryEntry:
     """Returned when getting an entry from the cache
 
     Attributes:
-        full (bool): Whether the cache has the full or dict or just some keys.
+        full: Whether the cache has the full or dict or just some keys.
             If not full then not all requested keys will necessarily be present
             in `value`
-        known_absent (set): Keys that were looked up in the dict and were not
+        known_absent: Keys that were looked up in the dict and were not
             there.
-        value (dict): The full or partial dict value
+        value: The full or partial dict value
     """
 
+    full = attr.ib(type=bool)
+    known_absent = attr.ib()
+    value = attr.ib()
+
     def __len__(self):
         return len(self.value)
 
@@ -45,21 +57,21 @@ class _Sentinel(enum.Enum):
     sentinel = object()
 
 
-class DictionaryCache:
+class DictionaryCache(Generic[KT, DKT]):
     """Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
     fetching a subset of dictionary keys for a particular key.
     """
 
-    def __init__(self, name, max_entries=1000):
+    def __init__(self, name: str, max_entries: int = 1000):
         self.cache = LruCache(
             max_size=max_entries, cache_name=name, size_callback=len
-        )  # type: LruCache[Any, DictionaryEntry]
+        )  # type: LruCache[KT, DictionaryEntry]
 
         self.name = name
         self.sequence = 0
-        self.thread = None
+        self.thread = None  # type: Optional[threading.Thread]
 
-    def check_thread(self):
+    def check_thread(self) -> None:
         expected_thread = self.thread
         if expected_thread is None:
             self.thread = threading.current_thread()
@@ -69,12 +81,14 @@ class DictionaryCache:
                     "Cache objects can only be accessed from the main thread"
                 )
 
-    def get(self, key, dict_keys=None):
+    def get(
+        self, key: KT, dict_keys: Optional[Iterable[DKT]] = None
+    ) -> DictionaryEntry:
         """Fetch an entry out of the cache
 
         Args:
             key
-            dict_key(list): If given a set of keys then return only those keys
+            dict_key: If given a set of keys then return only those keys
                 that exist in the cache.
 
         Returns:
@@ -95,7 +109,7 @@ class DictionaryCache:
 
         return DictionaryEntry(False, set(), {})
 
-    def invalidate(self, key):
+    def invalidate(self, key: KT) -> None:
         self.check_thread()
 
         # Increment the sequence number so that any SELECT statements that
@@ -103,19 +117,25 @@ class DictionaryCache:
         self.sequence += 1
         self.cache.pop(key, None)
 
-    def invalidate_all(self):
+    def invalidate_all(self) -> None:
         self.check_thread()
         self.sequence += 1
         self.cache.clear()
 
-    def update(self, sequence, key, value, fetched_keys=None):
+    def update(
+        self,
+        sequence: int,
+        key: KT,
+        value: Dict[DKT, Any],
+        fetched_keys: Optional[Set[DKT]] = None,
+    ) -> None:
         """Updates the entry in the cache
 
         Args:
             sequence
-            key (K)
-            value (dict[X,Y]): The value to update the cache with.
-            fetched_keys (None|set[X]): All of the dictionary keys which were
+            key
+            value: The value to update the cache with.
+            fetched_keys: All of the dictionary keys which were
                 fetched from the database.
 
                 If None, this is the complete value for key K. Otherwise, it
@@ -131,7 +151,9 @@ class DictionaryCache:
             else:
                 self._update_or_insert(key, value, fetched_keys)
 
-    def _update_or_insert(self, key, value, known_absent):
+    def _update_or_insert(
+        self, key: KT, value: Dict[DKT, Any], known_absent: Set[DKT]
+    ) -> None:
         # We pop and reinsert as we need to tell the cache the size may have
         # changed
 
@@ -140,5 +162,5 @@ class DictionaryCache:
         entry.known_absent.update(known_absent)
         self.cache[key] = entry
 
-    def _insert(self, key, value, known_absent):
+    def _insert(self, key: KT, value: Dict[DKT, Any], known_absent: Set[DKT]) -> None:
         self.cache[key] = DictionaryEntry(True, known_absent, value)
diff --git a/synapse/util/caches/ttlcache.py b/synapse/util/caches/ttlcache.py
index 6ce2a3d12..96a827494 100644
--- a/synapse/util/caches/ttlcache.py
+++ b/synapse/util/caches/ttlcache.py
@@ -15,6 +15,7 @@
 
 import logging
 import time
+from typing import Any, Callable, Dict, Generic, Tuple, TypeVar, Union
 
 import attr
 from sortedcontainers import SortedList
@@ -23,15 +24,19 @@ from synapse.util.caches import register_cache
 
 logger = logging.getLogger(__name__)
 
-SENTINEL = object()
+SENTINEL = object()  # type: Any
+
+T = TypeVar("T")
+KT = TypeVar("KT")
+VT = TypeVar("VT")
 
 
-class TTLCache:
+class TTLCache(Generic[KT, VT]):
     """A key/value cache implementation where each entry has its own TTL"""
 
-    def __init__(self, cache_name, timer=time.time):
+    def __init__(self, cache_name: str, timer: Callable[[], float] = time.time):
         # map from key to _CacheEntry
-        self._data = {}
+        self._data = {}  # type: Dict[KT, _CacheEntry]
 
         # the _CacheEntries, sorted by expiry time
         self._expiry_list = SortedList()  # type: SortedList[_CacheEntry]
@@ -40,26 +45,27 @@ class TTLCache:
 
         self._metrics = register_cache("ttl", cache_name, self, resizable=False)
 
-    def set(self, key, value, ttl):
+    def set(self, key: KT, value: VT, ttl: float) -> None:
         """Add/update an entry in the cache
 
         Args:
             key: key for this entry
             value: value for this entry
-            ttl (float): TTL for this entry, in seconds
+            ttl: TTL for this entry, in seconds
         """
         expiry = self._timer() + ttl
 
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e != SENTINEL:
+        if e is not SENTINEL:
+            assert isinstance(e, _CacheEntry)
             self._expiry_list.remove(e)
 
         entry = _CacheEntry(expiry_time=expiry, ttl=ttl, key=key, value=value)
         self._data[key] = entry
         self._expiry_list.add(entry)
 
-    def get(self, key, default=SENTINEL):
+    def get(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:
         """Get a value from the cache
 
         Args:
@@ -72,23 +78,23 @@ class TTLCache:
         """
         self.expire()
         e = self._data.get(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._metrics.inc_hits()
         return e.value
 
-    def get_with_expiry(self, key):
+    def get_with_expiry(self, key: KT) -> Tuple[VT, float, float]:
         """Get a value, and its expiry time, from the cache
 
         Args:
             key: key to look up
 
         Returns:
-            Tuple[Any, float, float]: the value from the cache, the expiry time
-            and the TTL
+            A tuple of  the value from the cache, the expiry time and the TTL
 
         Raises:
             KeyError if the entry is not found
@@ -102,7 +108,7 @@ class TTLCache:
         self._metrics.inc_hits()
         return e.value, e.expiry_time, e.ttl
 
-    def pop(self, key, default=SENTINEL):
+    def pop(self, key: KT, default: T = SENTINEL) -> Union[VT, T]:  # type: ignore
         """Remove a value from the cache
 
         If key is in the cache, remove it and return its value, else return default.
@@ -118,29 +124,30 @@ class TTLCache:
         """
         self.expire()
         e = self._data.pop(key, SENTINEL)
-        if e == SENTINEL:
+        if e is SENTINEL:
             self._metrics.inc_misses()
-            if default == SENTINEL:
+            if default is SENTINEL:
                 raise KeyError(key)
             return default
+        assert isinstance(e, _CacheEntry)
         self._expiry_list.remove(e)
         self._metrics.inc_hits()
         return e.value
 
-    def __getitem__(self, key):
+    def __getitem__(self, key: KT) -> VT:
         return self.get(key)
 
-    def __delitem__(self, key):
+    def __delitem__(self, key: KT) -> None:
         self.pop(key)
 
-    def __contains__(self, key):
+    def __contains__(self, key: KT) -> bool:
         return key in self._data
 
-    def __len__(self):
+    def __len__(self) -> int:
         self.expire()
         return len(self._data)
 
-    def expire(self):
+    def expire(self) -> None:
         """Run the expiry on the cache. Any entries whose expiry times are due will
         be removed
         """
@@ -158,7 +165,7 @@ class _CacheEntry:
     """TTLCache entry"""
 
     # expiry_time is the first attribute, so that entries are sorted by expiry.
-    expiry_time = attr.ib()
-    ttl = attr.ib()
+    expiry_time = attr.ib(type=float)
+    ttl = attr.ib(type=float)
     key = attr.ib()
     value = attr.ib()
diff --git a/tests/storage/test_state.py b/tests/storage/test_state.py
index 8bd12fa84..2471f1267 100644
--- a/tests/storage/test_state.py
+++ b/tests/storage/test_state.py
@@ -377,14 +377,11 @@ class StateStoreTestCase(tests.unittest.TestCase):
         #######################################################
         # deliberately remove e2 (room name) from the _state_group_cache
 
-        (
-            is_all,
-            known_absent,
-            state_dict_ids,
-        ) = self.state_datastore._state_group_cache.get(group)
+        cache_entry = self.state_datastore._state_group_cache.get(group)
+        state_dict_ids = cache_entry.value
 
-        self.assertEqual(is_all, True)
-        self.assertEqual(known_absent, set())
+        self.assertEqual(cache_entry.full, True)
+        self.assertEqual(cache_entry.known_absent, set())
         self.assertDictEqual(
             state_dict_ids,
             {
@@ -403,14 +400,11 @@ class StateStoreTestCase(tests.unittest.TestCase):
             fetched_keys=((e1.type, e1.state_key),),
         )
 
-        (
-            is_all,
-            known_absent,
-            state_dict_ids,
-        ) = self.state_datastore._state_group_cache.get(group)
+        cache_entry = self.state_datastore._state_group_cache.get(group)
+        state_dict_ids = cache_entry.value
 
-        self.assertEqual(is_all, False)
-        self.assertEqual(known_absent, {(e1.type, e1.state_key)})
+        self.assertEqual(cache_entry.full, False)
+        self.assertEqual(cache_entry.known_absent, {(e1.type, e1.state_key)})
         self.assertDictEqual(state_dict_ids, {(e1.type, e1.state_key): e1.event_id})
 
         ############################################
diff --git a/tests/util/test_dict_cache.py b/tests/util/test_dict_cache.py
index 34fdc9a43..2f41333f4 100644
--- a/tests/util/test_dict_cache.py
+++ b/tests/util/test_dict_cache.py
@@ -27,7 +27,9 @@ class DictCacheTestCase(unittest.TestCase):
         key = "test_simple_cache_hit_full"
 
         v = self.cache.get(key)
-        self.assertEqual((False, set(), {}), v)
+        self.assertIs(v.full, False)
+        self.assertEqual(v.known_absent, set())
+        self.assertEqual({}, v.value)
 
         seq = self.cache.sequence
         test_value = {"test": "test_simple_cache_hit_full"}