diff --git a/releasenotes/notes/annotate_code-197b93130df14042.yaml b/releasenotes/notes/annotate_code-197b93130df14042.yaml
new file mode 100644
index 0000000..faf4163
--- /dev/null
+++ b/releasenotes/notes/annotate_code-197b93130df14042.yaml
@@ -0,0 +1,3 @@
+---
+other:
+  - Add type annotations to cover all public API.
diff --git a/tenacity/__init__.py b/tenacity/__init__.py
index e258d8a..bc52383 100644
--- a/tenacity/__init__.py
+++ b/tenacity/__init__.py
@@ -89,6 +89,7 @@
 
 
 WrappedFn = t.TypeVar("WrappedFn", bound=t.Callable)
+_RetValT = t.TypeVar("_RetValT")
 
 
 @t.overload
@@ -388,14 +389,14 @@
                 break
 
     @abstractmethod
-    def __call__(self, fn: WrappedFn, *args: t.Any, **kwargs: t.Any) -> t.Any:
+    def __call__(self, fn: t.Callable[..., _RetValT], *args: t.Any, **kwargs: t.Any) -> _RetValT:
         pass
 
 
 class Retrying(BaseRetrying):
     """Retrying controller."""
 
-    def __call__(self, fn: WrappedFn, *args: t.Any, **kwargs: t.Any) -> t.Any:
+    def __call__(self, fn: t.Callable[..., _RetValT], *args: t.Any, **kwargs: t.Any) -> _RetValT:
         self.begin()
 
         retry_state = RetryCallState(retry_object=self, fn=fn, args=args, kwargs=kwargs)
diff --git a/tenacity/_asyncio.py b/tenacity/_asyncio.py
index 7b2447d..374ef20 100644
--- a/tenacity/_asyncio.py
+++ b/tenacity/_asyncio.py
@@ -17,6 +17,7 @@
 
 import functools
 import sys
+import typing
 from asyncio import sleep
 
 from tenacity import AttemptManager
@@ -25,13 +26,21 @@
 from tenacity import DoSleep
 from tenacity import RetryCallState
 
+WrappedFn = typing.TypeVar("WrappedFn", bound=typing.Callable)
+_RetValT = typing.TypeVar("_RetValT")
+
 
 class AsyncRetrying(BaseRetrying):
-    def __init__(self, sleep=sleep, **kwargs):
+    def __init__(self, sleep: typing.Callable[[float], typing.Awaitable] = sleep, **kwargs: typing.Any) -> None:
         super().__init__(**kwargs)
         self.sleep = sleep
 
-    async def __call__(self, fn, *args, **kwargs):
+    async def __call__(  # type: ignore  # Change signature from supertype
+        self,
+        fn: typing.Callable[..., typing.Awaitable[_RetValT]],
+        *args: typing.Any,
+        **kwargs: typing.Any,
+    ) -> _RetValT:
         self.begin()
 
         retry_state = RetryCallState(retry_object=self, fn=fn, args=args, kwargs=kwargs)
@@ -50,12 +59,12 @@
             else:
                 return do
 
-    def __aiter__(self):
+    def __aiter__(self) -> "AsyncRetrying":
         self.begin()
         self._retry_state = RetryCallState(self, fn=None, args=(), kwargs={})
         return self
 
-    async def __anext__(self):
+    async def __anext__(self) -> typing.Union[AttemptManager, typing.Any]:
         while True:
             do = self.iter(retry_state=self._retry_state)
             if do is None:
@@ -68,12 +77,12 @@
             else:
                 return do
 
-    def wraps(self, fn):
+    def wraps(self, fn: WrappedFn) -> WrappedFn:
         fn = super().wraps(fn)
         # Ensure wrapper is recognized as a coroutine function.
 
         @functools.wraps(fn)
-        async def async_wrapped(*args, **kwargs):
+        async def async_wrapped(*args: typing.Any, **kwargs: typing.Any) -> typing.Any:
             return await fn(*args, **kwargs)
 
         # Preserve attributes
diff --git a/tenacity/tornadoweb.py b/tenacity/tornadoweb.py
index 1175bec..9d7b395 100644
--- a/tenacity/tornadoweb.py
+++ b/tenacity/tornadoweb.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import sys
+import typing
 
 from tenacity import BaseRetrying
 from tenacity import DoAttempt
@@ -21,14 +22,24 @@
 
 from tornado import gen
 
+if typing.TYPE_CHECKING:
+    from tornado.concurrent import Future
+
+_RetValT = typing.TypeVar("_RetValT")
+
 
 class TornadoRetrying(BaseRetrying):
-    def __init__(self, sleep=gen.sleep, **kwargs):
+    def __init__(self, sleep: "typing.Callable[[float], Future[None]]" = gen.sleep, **kwargs: typing.Any) -> None:
         super().__init__(**kwargs)
         self.sleep = sleep
 
     @gen.coroutine
-    def __call__(self, fn, *args, **kwargs):
+    def __call__(  # type: ignore  # Change signature from supertype
+        self,
+        fn: "typing.Callable[..., typing.Union[typing.Generator[typing.Any, typing.Any, _RetValT], Future[_RetValT]]]",
+        *args: typing.Any,
+        **kwargs: typing.Any,
+    ) -> "typing.Generator[typing.Any, typing.Any, _RetValT]":
         self.begin()
 
         retry_state = RetryCallState(retry_object=self, fn=fn, args=args, kwargs=kwargs)
diff --git a/tenacity/wait.py b/tenacity/wait.py
index 2c1f4fb..aacb58d 100644
--- a/tenacity/wait.py
+++ b/tenacity/wait.py
@@ -111,7 +111,12 @@
     (and restricting the upper limit to some maximum value).
     """
 
-    def __init__(self, start=0, increment=100, max=_utils.MAX_WAIT):  # noqa
+    def __init__(
+        self,
+        start: typing.Union[int, float] = 0,
+        increment: typing.Union[int, float] = 100,
+        max: typing.Union[int, float] = _utils.MAX_WAIT,  # noqa
+    ) -> None:
         self.start = start
         self.increment = increment
         self.max = max
@@ -134,7 +139,13 @@
     wait_random_exponential for the latter case.
     """
 
-    def __init__(self, multiplier=1, max=_utils.MAX_WAIT, exp_base=2, min=0):  # noqa
+    def __init__(
+        self,
+        multiplier: typing.Union[int, float] = 1,
+        max: typing.Union[int, float] = _utils.MAX_WAIT,  # noqa
+        exp_base: typing.Union[int, float] = 2,
+        min: typing.Union[int, float] = 0,  # noqa
+    ) -> None:
         self.multiplier = multiplier
         self.min = min
         self.max = max