diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index d4e4e14..4f8992a 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -59,12 +59,15 @@ jobs:
     - name: Install test dependencies
       run: python -m pip install --upgrade tox codecov
 
+    - name: Check style and typing
+      if: startsWith(matrix.os, 'ubuntu-') && matrix.python-version == env.PYTHON_VERSION_BUILD_EXTRA
+      run: tox -e lint,typing
+
     - name: Run tests
-      run: tox -e ${PYTHON_VERSION},bench
+      run: tox -e ${PYTHON_VERSION}
 
-    - name: Lint
-      if: startsWith(matrix.os, 'ubuntu-') && matrix.python-version == env.PYTHON_VERSION_BUILD_EXTRA && always()
-      run: tox -e lint
+    - name: Run benchmarks
+      run: tox -e bench
 
     - name: Upload coverage
       run: codecov -X gcov
diff --git a/.gitignore b/.gitignore
index 0124316..8d65801 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@
 /.coverage
 /.eggs
 /.idea
+/.mypy_cache
 /.tox
 /coincurve.egg-info
 /build
diff --git a/coincurve/context.py b/coincurve/context.py
index b01bd80..c88be3d 100644
--- a/coincurve/context.py
+++ b/coincurve/context.py
@@ -7,7 +7,7 @@ from ._libsecp256k1 import ffi, lib
 
 
 class Context:
-    def __init__(self, seed=None, flag=CONTEXT_ALL):
+    def __init__(self, seed: bytes = None, flag=CONTEXT_ALL):
         if flag not in CONTEXT_FLAGS:
             raise ValueError('{} is an invalid context flag.'.format(flag))
         self._lock = Lock()
@@ -15,7 +15,7 @@ class Context:
         self.ctx = ffi.gc(lib.secp256k1_context_create(flag), lib.secp256k1_context_destroy)
         self.reseed(seed)
 
-    def reseed(self, seed=None):
+    def reseed(self, seed: bytes = None):
         """
         Protects against certain possible future side-channel timing attacks.
         """
diff --git a/coincurve/ecdsa.py b/coincurve/ecdsa.py
index 8d14bd0..5dd0b91 100644
--- a/coincurve/ecdsa.py
+++ b/coincurve/ecdsa.py
@@ -1,4 +1,5 @@
-from coincurve.context import GLOBAL_CONTEXT
+from coincurve.context import GLOBAL_CONTEXT, Context
+from coincurve.types import Hasher
 from coincurve.utils import bytes_to_int, int_to_bytes, sha256
 
 from ._libsecp256k1 import ffi, lib
@@ -7,7 +8,7 @@ MAX_SIG_LENGTH = 72
 CDATA_SIG_LENGTH = 64
 
 
-def cdata_to_der(cdata, context=GLOBAL_CONTEXT):
+def cdata_to_der(cdata, context: Context = GLOBAL_CONTEXT) -> bytes:
     der = ffi.new('unsigned char[%d]' % MAX_SIG_LENGTH)
     der_length = ffi.new('size_t *', MAX_SIG_LENGTH)
 
@@ -16,7 +17,7 @@ def cdata_to_der(cdata, context=GLOBAL_CONTEXT):
     return bytes(ffi.buffer(der, der_length[0]))
 
 
-def der_to_cdata(der, context=GLOBAL_CONTEXT):
+def der_to_cdata(der: bytes, context: Context = GLOBAL_CONTEXT):
     cdata = ffi.new('secp256k1_ecdsa_signature *')
     parsed = lib.secp256k1_ecdsa_signature_parse_der(context.ctx, cdata, der, len(der))
 
@@ -26,7 +27,7 @@ def der_to_cdata(der, context=GLOBAL_CONTEXT):
     return cdata
 
 
-def recover(message, recover_sig, hasher=sha256, context=GLOBAL_CONTEXT):
+def recover(message: bytes, recover_sig, hasher: Hasher = sha256, context: Context = GLOBAL_CONTEXT):
     msg_hash = hasher(message) if hasher is not None else message
     if len(msg_hash) != 32:
         raise ValueError('Message hash must be 32 bytes long.')
@@ -38,7 +39,7 @@ def recover(message, recover_sig, hasher=sha256, context=GLOBAL_CONTEXT):
     raise Exception('failed to recover ECDSA public key')
 
 
-def serialize_recoverable(recover_sig, context=GLOBAL_CONTEXT):
+def serialize_recoverable(recover_sig, context: Context = GLOBAL_CONTEXT) -> bytes:
     output = ffi.new('unsigned char[%d]' % CDATA_SIG_LENGTH)
     recid = ffi.new('int *')
 
@@ -47,7 +48,7 @@ def serialize_recoverable(recover_sig, context=GLOBAL_CONTEXT):
     return bytes(ffi.buffer(output, CDATA_SIG_LENGTH)) + int_to_bytes(recid[0])
 
 
-def deserialize_recoverable(serialized, context=GLOBAL_CONTEXT):
+def deserialize_recoverable(serialized: bytes, context: Context = GLOBAL_CONTEXT):
     if len(serialized) != 65:
         raise ValueError('Serialized signature must be 65 bytes long.')
 
@@ -71,7 +72,7 @@ Warning:
 """
 
 
-def serialize_compact(raw_sig, context=GLOBAL_CONTEXT):  # no cov
+def serialize_compact(raw_sig, context: Context = GLOBAL_CONTEXT):  # no cov
     output = ffi.new('unsigned char[%d]' % CDATA_SIG_LENGTH)
 
     res = lib.secp256k1_ecdsa_signature_serialize_compact(context.ctx, output, raw_sig)
@@ -80,7 +81,7 @@ def serialize_compact(raw_sig, context=GLOBAL_CONTEXT):  # no cov
     return bytes(ffi.buffer(output, CDATA_SIG_LENGTH))
 
 
-def deserialize_compact(ser_sig, context=GLOBAL_CONTEXT):  # no cov
+def deserialize_compact(ser_sig: bytes, context: Context = GLOBAL_CONTEXT):  # no cov
     if len(ser_sig) != 64:
         raise Exception('invalid signature length')
 
@@ -91,15 +92,13 @@ def deserialize_compact(ser_sig, context=GLOBAL_CONTEXT):  # no cov
     return raw_sig
 
 
-def signature_normalize(raw_sig, context=GLOBAL_CONTEXT):  # no cov
+def signature_normalize(raw_sig, context: Context = GLOBAL_CONTEXT):  # no cov
     """
     Check and optionally convert a signature to a normalized lower-S form.
-    If check_only is True then the normalized signature is not returned.
 
     This function always return a tuple containing a boolean (True if
     not previously normalized or False if signature was already
-    normalized), and the normalized signature. When check_only is True,
-    the normalized signature returned is always None.
+    normalized), and the normalized signature.
     """
     sigout = ffi.new('secp256k1_ecdsa_signature *')
 
@@ -108,7 +107,7 @@ def signature_normalize(raw_sig, context=GLOBAL_CONTEXT):  # no cov
     return not not res, sigout
 
 
-def recoverable_convert(recover_sig, context=GLOBAL_CONTEXT):  # no cov
+def recoverable_convert(recover_sig, context: Context = GLOBAL_CONTEXT):  # no cov
     normal_sig = ffi.new('secp256k1_ecdsa_signature *')
 
     lib.secp256k1_ecdsa_recoverable_signature_convert(context.ctx, normal_sig, recover_sig)
diff --git a/coincurve/keys.py b/coincurve/keys.py
index 38ddc6a..e6cacf4 100644
--- a/coincurve/keys.py
+++ b/coincurve/keys.py
@@ -1,8 +1,11 @@
+from typing import Tuple
+
 from asn1crypto.keys import ECDomainParameters, ECPointBitString, ECPrivateKey, PrivateKeyAlgorithm, PrivateKeyInfo
 
-from coincurve.context import GLOBAL_CONTEXT
+from coincurve.context import GLOBAL_CONTEXT, Context
 from coincurve.ecdsa import cdata_to_der, der_to_cdata, deserialize_recoverable, recover, serialize_recoverable
 from coincurve.flags import EC_COMPRESSED, EC_UNCOMPRESSED
+from coincurve.types import Hasher
 from coincurve.utils import (
     bytes_to_int,
     der_to_pem,
@@ -21,12 +24,12 @@ DEFAULT_NONCE = (ffi.NULL, ffi.NULL)
 
 
 class PrivateKey:
-    def __init__(self, secret=None, context=GLOBAL_CONTEXT):
-        self.secret = validate_secret(secret) if secret is not None else get_valid_secret()
+    def __init__(self, secret: bytes = None, context: Context = GLOBAL_CONTEXT):
+        self.secret: bytes = validate_secret(secret) if secret is not None else get_valid_secret()
         self.context = context
-        self.public_key = PublicKey.from_valid_secret(self.secret, self.context)
+        self.public_key: PublicKey = PublicKey.from_valid_secret(self.secret, self.context)
 
-    def sign(self, message, hasher=sha256, custom_nonce=None):
+    def sign(self, message: bytes, hasher: Hasher = sha256, custom_nonce=None) -> bytes:
         msg_hash = hasher(message) if hasher is not None else message
         if len(msg_hash) != 32:
             raise ValueError('Message hash must be 32 bytes long.')
@@ -41,7 +44,7 @@ class PrivateKey:
 
         return cdata_to_der(signature, self.context)
 
-    def sign_recoverable(self, message, hasher=sha256):
+    def sign_recoverable(self, message, hasher: Hasher = sha256):
         msg_hash = hasher(message) if hasher is not None else message
         if len(msg_hash) != 32:
             raise ValueError('Message hash must be 32 bytes long.')
@@ -57,14 +60,14 @@ class PrivateKey:
 
         return serialize_recoverable(signature, self.context)
 
-    def ecdh(self, public_key):
+    def ecdh(self, public_key: bytes) -> bytes:
         secret = ffi.new('unsigned char [32]')
 
         lib.secp256k1_ecdh(self.context.ctx, secret, PublicKey(public_key).public_key, self.secret, ffi.NULL, ffi.NULL)
 
         return bytes(ffi.buffer(secret, 32))
 
-    def add(self, scalar, update=False):
+    def add(self, scalar: bytes, update=False):
         scalar = pad_scalar(scalar)
 
         secret = ffi.new('unsigned char [32]', self.secret)
@@ -83,7 +86,7 @@ class PrivateKey:
 
         return PrivateKey(secret, self.context)
 
-    def multiply(self, scalar, update=False):
+    def multiply(self, scalar: bytes, update=False):
         scalar = validate_secret(scalar)
 
         secret = ffi.new('unsigned char [32]', self.secret)
@@ -99,16 +102,16 @@ class PrivateKey:
 
         return PrivateKey(secret, self.context)
 
-    def to_hex(self):
+    def to_hex(self) -> str:
         return self.secret.hex()
 
-    def to_int(self):
+    def to_int(self) -> int:
         return bytes_to_int(self.secret)
 
-    def to_pem(self):
+    def to_pem(self) -> bytes:
         return der_to_pem(self.to_der())
 
-    def to_der(self):
+    def to_der(self) -> bytes:
         pk = ECPrivateKey(
             {
                 'version': 'ecPrivkeyVer1',
@@ -131,21 +134,21 @@ class PrivateKey:
         ).dump()
 
     @classmethod
-    def from_hex(cls, hexed, context=GLOBAL_CONTEXT):
+    def from_hex(cls, hexed: str, context: Context = GLOBAL_CONTEXT):
         return PrivateKey(hex_to_bytes(hexed), context)
 
     @classmethod
-    def from_int(cls, num, context=GLOBAL_CONTEXT):
+    def from_int(cls, num: int, context: Context = GLOBAL_CONTEXT):
         return PrivateKey(int_to_bytes_padded(num), context)
 
     @classmethod
-    def from_pem(cls, pem, context=GLOBAL_CONTEXT):
+    def from_pem(cls, pem: bytes, context: Context = GLOBAL_CONTEXT):
         return PrivateKey(
             int_to_bytes_padded(PrivateKeyInfo.load(pem_to_der(pem)).native['private_key']['private_key']), context
         )
 
     @classmethod
-    def from_der(cls, der, context=GLOBAL_CONTEXT):
+    def from_der(cls, der: bytes, context: Context = GLOBAL_CONTEXT):
         return PrivateKey(int_to_bytes_padded(PrivateKeyInfo.load(der).native['private_key']['private_key']), context)
 
     def _update_public_key(self):
@@ -154,12 +157,12 @@ class PrivateKey:
         if not created:
             raise ValueError('Invalid secret.')
 
-    def __eq__(self, other):
+    def __eq__(self, other) -> bool:
         return self.secret == other.secret
 
 
 class PublicKey:
-    def __init__(self, data, context=GLOBAL_CONTEXT):
+    def __init__(self, data, context: Context = GLOBAL_CONTEXT):
         if not isinstance(data, bytes):
             self.public_key = data
         else:
@@ -175,7 +178,7 @@ class PublicKey:
         self.context = context
 
     @classmethod
-    def from_secret(cls, secret, context=GLOBAL_CONTEXT):
+    def from_secret(cls, secret: bytes, context: Context = GLOBAL_CONTEXT):
         public_key = ffi.new('secp256k1_pubkey *')
 
         created = lib.secp256k1_ec_pubkey_create(context.ctx, public_key, validate_secret(secret))
@@ -190,7 +193,7 @@ class PublicKey:
         return PublicKey(public_key, context)
 
     @classmethod
-    def from_valid_secret(cls, secret, context=GLOBAL_CONTEXT):
+    def from_valid_secret(cls, secret: bytes, context: Context = GLOBAL_CONTEXT):
         public_key = ffi.new('secp256k1_pubkey *')
 
         created = lib.secp256k1_ec_pubkey_create(context.ctx, public_key, secret)
@@ -201,17 +204,19 @@ class PublicKey:
         return PublicKey(public_key, context)
 
     @classmethod
-    def from_point(cls, x, y, context=GLOBAL_CONTEXT):
+    def from_point(cls, x: int, y: int, context: Context = GLOBAL_CONTEXT):
         return PublicKey(b'\x04' + int_to_bytes_padded(x) + int_to_bytes_padded(y), context)
 
     @classmethod
-    def from_signature_and_message(cls, serialized_sig, message, hasher=sha256, context=GLOBAL_CONTEXT):
+    def from_signature_and_message(
+        cls, serialized_sig: bytes, message: bytes, hasher: Hasher = sha256, context: Context = GLOBAL_CONTEXT
+    ):
         return PublicKey(
             recover(message, deserialize_recoverable(serialized_sig, context=context), hasher=hasher, context=context)
         )
 
     @classmethod
-    def combine_keys(cls, public_keys, context=GLOBAL_CONTEXT):
+    def combine_keys(cls, public_keys, context: Context = GLOBAL_CONTEXT):
         public_key = ffi.new('secp256k1_pubkey *')
 
         combined = lib.secp256k1_ec_pubkey_combine(
@@ -223,7 +228,7 @@ class PublicKey:
 
         return PublicKey(public_key, context)
 
-    def format(self, compressed=True):
+    def format(self, compressed=True) -> bytes:
         length = 33 if compressed else 65
         serialized = ffi.new('unsigned char [%d]' % length)
         output_len = ffi.new('size_t *', length)
@@ -234,11 +239,11 @@ class PublicKey:
 
         return bytes(ffi.buffer(serialized, length))
 
-    def point(self):
+    def point(self) -> Tuple[int, int]:
         public_key = self.format(compressed=False)
         return bytes_to_int(public_key[1:33]), bytes_to_int(public_key[33:])
 
-    def verify(self, signature, message, hasher=sha256):
+    def verify(self, signature: bytes, message: bytes, hasher: Hasher = sha256) -> bool:
         msg_hash = hasher(message) if hasher is not None else message
         if len(msg_hash) != 32:
             raise ValueError('Message hash must be 32 bytes long.')
@@ -248,7 +253,7 @@ class PublicKey:
         # A performance hack to avoid global bool() lookup.
         return not not verified
 
-    def add(self, scalar, update=False):
+    def add(self, scalar: bytes, update=False):
         scalar = pad_scalar(scalar)
 
         new_key = ffi.new('secp256k1_pubkey *', self.public_key[0])
@@ -264,7 +269,7 @@ class PublicKey:
 
         return PublicKey(new_key, self.context)
 
-    def multiply(self, scalar, update=False):
+    def multiply(self, scalar: bytes, update=False):
         scalar = validate_secret(scalar)
 
         new_key = ffi.new('secp256k1_pubkey *', self.public_key[0])
@@ -293,5 +298,5 @@ class PublicKey:
 
         return PublicKey(new_key, self.context)
 
-    def __eq__(self, other):
+    def __eq__(self, other) -> bool:
         return self.format(compressed=False) == other.format(compressed=False)
diff --git a/coincurve/types.py b/coincurve/types.py
new file mode 100644
index 0000000..123baed
--- /dev/null
+++ b/coincurve/types.py
@@ -0,0 +1,10 @@
+import sys
+from typing import Optional
+
+# https://bugs.python.org/issue42965
+if sys.version_info >= (3, 9, 2):
+    from collections.abc import Callable
+else:
+    from typing import Callable
+
+Hasher = Optional[Callable[[bytes], bytes]]
diff --git a/coincurve/utils.py b/coincurve/utils.py
index d803048..44e728a 100644
--- a/coincurve/utils.py
+++ b/coincurve/utils.py
@@ -1,8 +1,10 @@
 from base64 import b64decode, b64encode
 from hashlib import sha256 as _sha256
 from os import urandom
+from typing import Generator
 
-from coincurve.context import GLOBAL_CONTEXT
+from coincurve.context import GLOBAL_CONTEXT, Context
+from coincurve.types import Hasher
 
 from ._libsecp256k1 import ffi, lib
 
@@ -17,61 +19,63 @@ PEM_HEADER = b'-----BEGIN PRIVATE KEY-----\n'
 PEM_FOOTER = b'-----END PRIVATE KEY-----\n'
 
 
-def pad_hex(hexed):
+def pad_hex(hexed: str) -> str:
     # Pad odd-length hex strings.
     return hexed if not len(hexed) & 1 else f'0{hexed}'
 
 
-def bytes_to_int(bytestr):
+def bytes_to_int(bytestr: bytes) -> int:
     return int.from_bytes(bytestr, 'big')
 
 
-def int_to_bytes(num):
+def int_to_bytes(num: int) -> bytes:
     return num.to_bytes((num.bit_length() + 7) // 8 or 1, 'big')
 
 
-def int_to_bytes_padded(num):
+def int_to_bytes_padded(num: int) -> bytes:
     return pad_scalar(num.to_bytes((num.bit_length() + 7) // 8 or 1, 'big'))
 
 
-def hex_to_bytes(hexed):
+def hex_to_bytes(hexed: str) -> bytes:
     return pad_scalar(bytes.fromhex(pad_hex(hexed)))
 
 
-def sha256(bytestr):
+def sha256(bytestr: bytes) -> bytes:
     return _sha256(bytestr).digest()
 
 
-def chunk_data(data, size):
+def chunk_data(data: bytes, size: int) -> Generator[bytes, None, None]:
     return (data[i : i + size] for i in range(0, len(data), size))
 
 
-def der_to_pem(der):
+def der_to_pem(der: bytes) -> bytes:
     return b''.join([PEM_HEADER, b'\n'.join(chunk_data(b64encode(der), 64)), b'\n', PEM_FOOTER])
 
 
-def pem_to_der(pem):
+def pem_to_der(pem: bytes) -> bytes:
     return b64decode(b''.join(pem.strip().splitlines()[1:-1]))
 
 
-def get_valid_secret():
+def get_valid_secret() -> bytes:
     while True:
         secret = urandom(KEY_SIZE)
         if ZERO < secret < GROUP_ORDER:
             return secret
 
 
-def pad_scalar(scalar):
+def pad_scalar(scalar: bytes) -> bytes:
     return (ZERO * (KEY_SIZE - len(scalar))) + scalar
 
 
-def validate_secret(secret):
+def validate_secret(secret: bytes) -> bytes:
     if not 0 < bytes_to_int(secret) < GROUP_ORDER_INT:
         raise ValueError('Secret scalar must be greater than 0 and less than {}.'.format(GROUP_ORDER_INT))
     return pad_scalar(secret)
 
 
-def verify_signature(signature, message, public_key, hasher=sha256, context=GLOBAL_CONTEXT):
+def verify_signature(
+    signature: bytes, message: bytes, public_key: bytes, hasher: Hasher = sha256, context: Context = GLOBAL_CONTEXT
+) -> bool:
     pubkey = ffi.new('secp256k1_pubkey *')
 
     pubkey_parsed = lib.secp256k1_ec_pubkey_parse(context.ctx, pubkey, public_key, len(public_key))
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..1772231
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,8 @@
+[mypy]
+disallow_untyped_defs = false
+follow_imports = normal
+ignore_missing_imports = true
+pretty = true
+show_column_numbers = true
+warn_no_return = false
+warn_unused_ignores = true
diff --git a/tox.ini b/tox.ini
index 2094575..e094bb8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,7 @@ envlist =
     bench
     lint
     fmt
+    typing
 
 [testenv]
 passenv = *
@@ -51,3 +52,10 @@ commands =
     isort .
     black .
     {[testenv:lint]commands}
+
+[testenv:typing]
+skip_install = true
+deps =
+    mypy==0.790
+commands =
+    mypy coincurve