diff --git a/immutabledict/__init__.py b/immutabledict/__init__.py
index 57ed231..0cbdac4 100644
--- a/immutabledict/__init__.py
+++ b/immutabledict/__init__.py
@@ -1,10 +1,27 @@
+import sys
 from collections import OrderedDict
-from collections.abc import Mapping
+from typing import Dict, TypeVar
+
+if sys.version_info >= (3, 7):
+    from typing import Mapping
+else:  # pragma: no cover
+    from collections.abc import Mapping as _BaseMapping
+
+    class _MappingMeta(type):
+        def __getitem__(self, *args):
+            return _BaseMapping
+
+    class Mapping(metaclass=_MappingMeta):
+        pass
+
 
 __version__ = "1.2.0"
 
+_K = TypeVar("_K")
+_V = TypeVar("_V")
+
 
-class immutabledict(Mapping):
+class immutabledict(Mapping[_K, _V]):
     """
     An immutable wrapper around dictionaries that implements the complete :py:class:`collections.Mapping`
     interface. It can be used as a drop-in replacement for dictionaries where immutability is desired.
@@ -26,7 +43,7 @@ def __getitem__(self, key):
     def __contains__(self, key):
         return key in self._dict
 
-    def copy(self, **add_or_replace):
+    def copy(self, **add_or_replace: Dict[_K, _V]) -> "immutabledict[_K, _V]":
         return self.__class__(self, **add_or_replace)
 
     def __iter__(self):
diff --git a/immutabledict/py.typed b/immutabledict/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/poetry.lock b/poetry.lock
index 832888f..44a8a8b 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -86,6 +86,22 @@ category = "dev"
 optional = false
 python-versions = ">=3.6, <3.7"
 
+[[package]]
+name = "distlib"
+version = "0.3.1"
+description = "Distribution utilities"
+category = "dev"
+optional = false
+python-versions = "*"
+
+[[package]]
+name = "filelock"
+version = "3.0.12"
+description = "A platform independent file lock."
+category = "dev"
+optional = false
+python-versions = "*"
+
 [[package]]
 name = "importlib-metadata"
 version = "3.7.0"
@@ -102,6 +118,21 @@ zipp = ">=0.5"
 docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
 testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "pytest-enabler", "packaging", "pep517", "pyfakefs", "flufl.flake8", "pytest-black (>=0.3.7)", "pytest-mypy", "importlib-resources (>=1.3)"]
 
+[[package]]
+name = "importlib-resources"
+version = "5.1.2"
+description = "Read resources from Python packages"
+category = "dev"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+zipp = {version = ">=0.4", markers = "python_version < \"3.8\""}
+
+[package.extras]
+docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
+testing = ["pytest (>=4.6)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "pytest-enabler", "pytest-black (>=0.3.7)", "pytest-mypy"]
+
 [[package]]
 name = "iniconfig"
 version = "1.1.1"
@@ -123,6 +154,22 @@ pipfile_deprecated_finder = ["pipreqs", "requirementslib"]
 requirements_deprecated_finder = ["pipreqs", "pip-api"]
 colors = ["colorama (>=0.4.3,<0.5.0)"]
 
+[[package]]
+name = "mypy"
+version = "0.812"
+description = "Optional static typing for Python"
+category = "dev"
+optional = false
+python-versions = ">=3.5"
+
+[package.dependencies]
+mypy-extensions = ">=0.4.3,<0.5.0"
+typed-ast = ">=1.4.0,<1.5.0"
+typing-extensions = ">=3.7.4"
+
+[package.extras]
+dmypy = ["psutil (>=4.0)"]
+
 [[package]]
 name = "mypy-extensions"
 version = "0.4.3"
@@ -225,6 +272,14 @@ category = "dev"
 optional = false
 python-versions = "*"
 
+[[package]]
+name = "six"
+version = "1.15.0"
+description = "Python 2 and 3 compatibility utilities"
+category = "dev"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*"
+
 [[package]]
 name = "toml"
 version = "0.10.2"
@@ -233,6 +288,29 @@ category = "dev"
 optional = false
 python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
 
+[[package]]
+name = "tox"
+version = "3.23.0"
+description = "tox is a generic virtualenv management and test command line tool"
+category = "dev"
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,>=2.7"
+
+[package.dependencies]
+colorama = {version = ">=0.4.1", markers = "platform_system == \"Windows\""}
+filelock = ">=3.0.0"
+importlib-metadata = {version = ">=0.12", markers = "python_version < \"3.8\""}
+packaging = ">=14"
+pluggy = ">=0.12.0"
+py = ">=1.4.17"
+six = ">=1.14.0"
+toml = ">=0.9.4"
+virtualenv = ">=16.0.0,<20.0.0 || >20.0.0,<20.0.1 || >20.0.1,<20.0.2 || >20.0.2,<20.0.3 || >20.0.3,<20.0.4 || >20.0.4,<20.0.5 || >20.0.5,<20.0.6 || >20.0.6,<20.0.7 || >20.0.7"
+
+[package.extras]
+docs = ["pygments-github-lexers (>=0.0.5)", "sphinx (>=2.0.0)", "sphinxcontrib-autoprogram (>=0.1.5)", "towncrier (>=18.5.0)"]
+testing = ["flaky (>=3.4.0)", "freezegun (>=0.3.11)", "psutil (>=5.6.1)", "pytest (>=4.0.0)", "pytest-cov (>=2.5.1)", "pytest-mock (>=1.10.0)", "pytest-randomly (>=1.0.0)", "pytest-xdist (>=1.22.2)", "pathlib2 (>=2.3.3)"]
+
 [[package]]
 name = "typed-ast"
 version = "1.4.2"
@@ -249,6 +327,26 @@ category = "dev"
 optional = false
 python-versions = "*"
 
+[[package]]
+name = "virtualenv"
+version = "20.4.3"
+description = "Virtual Python Environment builder"
+category = "dev"
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,>=2.7"
+
+[package.dependencies]
+appdirs = ">=1.4.3,<2"
+distlib = ">=0.3.1,<1"
+filelock = ">=3.0.0,<4"
+importlib-metadata = {version = ">=0.12", markers = "python_version < \"3.8\""}
+importlib-resources = {version = ">=1.0", markers = "python_version < \"3.7\""}
+six = ">=1.9.0,<2"
+
+[package.extras]
+docs = ["proselint (>=0.10.2)", "sphinx (>=3)", "sphinx-argparse (>=0.2.5)", "sphinx-rtd-theme (>=0.4.3)", "towncrier (>=19.9.0rc1)"]
+testing = ["coverage (>=4)", "coverage-enable-subprocess (>=1)", "flaky (>=3)", "pytest (>=4)", "pytest-env (>=0.6.2)", "pytest-freezegun (>=0.4.1)", "pytest-mock (>=2)", "pytest-randomly (>=1)", "pytest-timeout (>=1)", "packaging (>=20.0)", "xonsh (>=0.9.16)"]
+
 [[package]]
 name = "zipp"
 version = "3.4.1"
@@ -264,7 +362,7 @@ testing = ["pytest (>=4.6)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pyt
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.6"
-content-hash = "958eb260e96ae8a6de2cc8caf15cab2c5e89cc71eb0ef39d72a040bafb35935b"
+content-hash = "e9dc552c0e42f4e4806fea31573c5bfd4068f71c8c990afb2b1e3a97a58d11c4"
 
 [metadata.files]
 appdirs = [
@@ -348,10 +446,22 @@ dataclasses = [
     {file = "dataclasses-0.8-py3-none-any.whl", hash = "sha256:0201d89fa866f68c8ebd9d08ee6ff50c0b255f8ec63a71c16fda7af82bb887bf"},
     {file = "dataclasses-0.8.tar.gz", hash = "sha256:8479067f342acf957dc82ec415d355ab5edb7e7646b90dc6e2fd1d96ad084c97"},
 ]
+distlib = [
+    {file = "distlib-0.3.1-py2.py3-none-any.whl", hash = "sha256:8c09de2c67b3e7deef7184574fc060ab8a793e7adbb183d942c389c8b13c52fb"},
+    {file = "distlib-0.3.1.zip", hash = "sha256:edf6116872c863e1aa9d5bb7cb5e05a022c519a4594dc703843343a9ddd9bff1"},
+]
+filelock = [
+    {file = "filelock-3.0.12-py3-none-any.whl", hash = "sha256:929b7d63ec5b7d6b71b0fa5ac14e030b3f70b75747cef1b10da9b879fef15836"},
+    {file = "filelock-3.0.12.tar.gz", hash = "sha256:18d82244ee114f543149c66a6e0c14e9c4f8a1044b5cdaadd0f82159d6a6ff59"},
+]
 importlib-metadata = [
     {file = "importlib_metadata-3.7.0-py3-none-any.whl", hash = "sha256:c6af5dbf1126cd959c4a8d8efd61d4d3c83bddb0459a17e554284a077574b614"},
     {file = "importlib_metadata-3.7.0.tar.gz", hash = "sha256:24499ffde1b80be08284100393955842be4a59c7c16bbf2738aad0e464a8e0aa"},
 ]
+importlib-resources = [
+    {file = "importlib_resources-5.1.2-py3-none-any.whl", hash = "sha256:ebab3efe74d83b04d6bf5cd9a17f0c5c93e60fb60f30c90f56265fce4682a469"},
+    {file = "importlib_resources-5.1.2.tar.gz", hash = "sha256:642586fc4740bd1cad7690f836b3321309402b20b332529f25617ff18e8e1370"},
+]
 iniconfig = [
     {file = "iniconfig-1.1.1-py2.py3-none-any.whl", hash = "sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3"},
     {file = "iniconfig-1.1.1.tar.gz", hash = "sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32"},
@@ -360,6 +470,30 @@ isort = [
     {file = "isort-5.8.0-py3-none-any.whl", hash = "sha256:2bb1680aad211e3c9944dbce1d4ba09a989f04e238296c87fe2139faa26d655d"},
     {file = "isort-5.8.0.tar.gz", hash = "sha256:0a943902919f65c5684ac4e0154b1ad4fac6dcaa5d9f3426b732f1c8b5419be6"},
 ]
+mypy = [
+    {file = "mypy-0.812-cp35-cp35m-macosx_10_9_x86_64.whl", hash = "sha256:a26f8ec704e5a7423c8824d425086705e381b4f1dfdef6e3a1edab7ba174ec49"},
+    {file = "mypy-0.812-cp35-cp35m-manylinux1_x86_64.whl", hash = "sha256:28fb5479c494b1bab244620685e2eb3c3f988d71fd5d64cc753195e8ed53df7c"},
+    {file = "mypy-0.812-cp35-cp35m-manylinux2010_x86_64.whl", hash = "sha256:9743c91088d396c1a5a3c9978354b61b0382b4e3c440ce83cf77994a43e8c521"},
+    {file = "mypy-0.812-cp35-cp35m-win_amd64.whl", hash = "sha256:d7da2e1d5f558c37d6e8c1246f1aec1e7349e4913d8fb3cb289a35de573fe2eb"},
+    {file = "mypy-0.812-cp36-cp36m-macosx_10_9_x86_64.whl", hash = "sha256:4eec37370483331d13514c3f55f446fc5248d6373e7029a29ecb7b7494851e7a"},
+    {file = "mypy-0.812-cp36-cp36m-manylinux1_x86_64.whl", hash = "sha256:d65cc1df038ef55a99e617431f0553cd77763869eebdf9042403e16089fe746c"},
+    {file = "mypy-0.812-cp36-cp36m-manylinux2010_x86_64.whl", hash = "sha256:61a3d5b97955422964be6b3baf05ff2ce7f26f52c85dd88db11d5e03e146a3a6"},
+    {file = "mypy-0.812-cp36-cp36m-win_amd64.whl", hash = "sha256:25adde9b862f8f9aac9d2d11971f226bd4c8fbaa89fb76bdadb267ef22d10064"},
+    {file = "mypy-0.812-cp37-cp37m-macosx_10_9_x86_64.whl", hash = "sha256:552a815579aa1e995f39fd05dde6cd378e191b063f031f2acfe73ce9fb7f9e56"},
+    {file = "mypy-0.812-cp37-cp37m-manylinux1_x86_64.whl", hash = "sha256:499c798053cdebcaa916eef8cd733e5584b5909f789de856b482cd7d069bdad8"},
+    {file = "mypy-0.812-cp37-cp37m-manylinux2010_x86_64.whl", hash = "sha256:5873888fff1c7cf5b71efbe80e0e73153fe9212fafdf8e44adfe4c20ec9f82d7"},
+    {file = "mypy-0.812-cp37-cp37m-win_amd64.whl", hash = "sha256:9f94aac67a2045ec719ffe6111df543bac7874cee01f41928f6969756e030564"},
+    {file = "mypy-0.812-cp38-cp38-macosx_10_9_x86_64.whl", hash = "sha256:d23e0ea196702d918b60c8288561e722bf437d82cb7ef2edcd98cfa38905d506"},
+    {file = "mypy-0.812-cp38-cp38-manylinux1_x86_64.whl", hash = "sha256:674e822aa665b9fd75130c6c5f5ed9564a38c6cea6a6432ce47eafb68ee578c5"},
+    {file = "mypy-0.812-cp38-cp38-manylinux2010_x86_64.whl", hash = "sha256:abf7e0c3cf117c44d9285cc6128856106183938c68fd4944763003decdcfeb66"},
+    {file = "mypy-0.812-cp38-cp38-win_amd64.whl", hash = "sha256:0d0a87c0e7e3a9becdfbe936c981d32e5ee0ccda3e0f07e1ef2c3d1a817cf73e"},
+    {file = "mypy-0.812-cp39-cp39-macosx_10_9_x86_64.whl", hash = "sha256:7ce3175801d0ae5fdfa79b4f0cfed08807af4d075b402b7e294e6aa72af9aa2a"},
+    {file = "mypy-0.812-cp39-cp39-manylinux1_x86_64.whl", hash = "sha256:b09669bcda124e83708f34a94606e01b614fa71931d356c1f1a5297ba11f110a"},
+    {file = "mypy-0.812-cp39-cp39-manylinux2010_x86_64.whl", hash = "sha256:33f159443db0829d16f0a8d83d94df3109bb6dd801975fe86bacb9bf71628e97"},
+    {file = "mypy-0.812-cp39-cp39-win_amd64.whl", hash = "sha256:3f2aca7f68580dc2508289c729bd49ee929a436208d2b2b6aab15745a70a57df"},
+    {file = "mypy-0.812-py3-none-any.whl", hash = "sha256:2f9b3407c58347a452fc0736861593e105139b905cca7d097e413453a1d650b4"},
+    {file = "mypy-0.812.tar.gz", hash = "sha256:cd07039aa5df222037005b08fbbfd69b3ab0b0bd7a07d7906de75ae52c4e3119"},
+]
 mypy-extensions = [
     {file = "mypy_extensions-0.4.3-py2.py3-none-any.whl", hash = "sha256:090fedd75945a69ae91ce1303b5824f428daf5a028d2f6ab8a299250a846f15d"},
     {file = "mypy_extensions-0.4.3.tar.gz", hash = "sha256:2d82818f5bb3e369420cb3c4060a7970edba416647068eb4c5343488a6c604a8"},
@@ -435,10 +569,18 @@ regex = [
     {file = "regex-2020.11.13-cp39-cp39-win_amd64.whl", hash = "sha256:a15f64ae3a027b64496a71ab1f722355e570c3fac5ba2801cafce846bf5af01d"},
     {file = "regex-2020.11.13.tar.gz", hash = "sha256:83d6b356e116ca119db8e7c6fc2983289d87b27b3fac238cfe5dca529d884562"},
 ]
+six = [
+    {file = "six-1.15.0-py2.py3-none-any.whl", hash = "sha256:8b74bedcbbbaca38ff6d7491d76f2b06b3592611af620f8426e82dddb04a5ced"},
+    {file = "six-1.15.0.tar.gz", hash = "sha256:30639c035cdb23534cd4aa2dd52c3bf48f06e5f4a941509c8bafd8ce11080259"},
+]
 toml = [
     {file = "toml-0.10.2-py2.py3-none-any.whl", hash = "sha256:806143ae5bfb6a3c6e736a764057db0e6a0e05e338b5630894a5f779cabb4f9b"},
     {file = "toml-0.10.2.tar.gz", hash = "sha256:b3bda1d108d5dd99f4a20d24d9c348e91c4db7ab1b749200bded2f839ccbe68f"},
 ]
+tox = [
+    {file = "tox-3.23.0-py2.py3-none-any.whl", hash = "sha256:e007673f3595cede9b17a7c4962389e4305d4a3682a6c5a4159a1453b4f326aa"},
+    {file = "tox-3.23.0.tar.gz", hash = "sha256:05a4dbd5e4d3d8269b72b55600f0b0303e2eb47ad5c6fe76d3576f4c58d93661"},
+]
 typed-ast = [
     {file = "typed_ast-1.4.2-cp35-cp35m-manylinux1_i686.whl", hash = "sha256:7703620125e4fb79b64aa52427ec192822e9f45d37d4b6625ab37ef403e1df70"},
     {file = "typed_ast-1.4.2-cp35-cp35m-manylinux1_x86_64.whl", hash = "sha256:c9aadc4924d4b5799112837b226160428524a9a45f830e0d0f184b19e4090487"},
@@ -476,6 +618,10 @@ typing-extensions = [
     {file = "typing_extensions-3.7.4.3-py3-none-any.whl", hash = "sha256:7cb407020f00f7bfc3cb3e7881628838e69d8f3fcab2f64742a5e76b2f841918"},
     {file = "typing_extensions-3.7.4.3.tar.gz", hash = "sha256:99d4073b617d30288f569d3f13d2bd7548c3a7e4c8de87db09a9d29bb3a4a60c"},
 ]
+virtualenv = [
+    {file = "virtualenv-20.4.3-py2.py3-none-any.whl", hash = "sha256:83f95875d382c7abafe06bd2a4cdd1b363e1bb77e02f155ebe8ac082a916b37c"},
+    {file = "virtualenv-20.4.3.tar.gz", hash = "sha256:49ec4eb4c224c6f7dd81bb6d0a28a09ecae5894f4e593c89b0db0885f565a107"},
+]
 zipp = [
     {file = "zipp-3.4.1-py3-none-any.whl", hash = "sha256:51cb66cc54621609dd593d1787f286ee42a5c0adbb4b29abea5a63edc3e03098"},
     {file = "zipp-3.4.1.tar.gz", hash = "sha256:3607921face881ba3e026887d8150cca609d517579abe052ac81fc5aeffdbd76"},
diff --git a/pyproject.toml b/pyproject.toml
index cb1db99..c3a5b15 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,7 +23,9 @@ black = {version = "^20.8b1", python = "^3.6"}
 pytest = "^6.2"
 isort = {version = "^5.8", python = "^3.6"}
 pytest-cov = "^2.11"
+mypy = "^0.812"
+tox = "^3.23.0"
 
 [build-system]
-requires = ["poetry>=0.12"]
+requires = ["poetry>=1.1.5"]
 build-backend = "poetry.masonry.api"
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..47ce63e
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,9 @@
+[tox]
+isolated_build = true
+envlist = py36,py37,py38,py39
+
+[testenv]
+whitelist_externals = poetry
+commands =
+    poetry install -v
+    poetry run pytest tests/