diff --git a/.azuredevops/pull_request_template.md b/.azuredevops/pull_request_template.md
index 5ff03e18..fd28ed57 100644
--- a/.azuredevops/pull_request_template.md
+++ b/.azuredevops/pull_request_template.md
@@ -9,4 +9,5 @@
 - [ ] I have performed **self-review** of the code
 - [ ] I have written **tests** for any new functionality added with this PR
 - [ ] I have updated the **documentation** if this PR changes or adds functionality
+- [ ] I have written/updated **design docs** if this PR implements new functionality.
 - [ ] I have run **pre-commit** checks for code style
diff --git a/.flake8 b/.flake8
index 398d14fb..6e653102 100644
--- a/.flake8
+++ b/.flake8
@@ -9,5 +9,8 @@ extend-ignore =
     E712
     D401
     F811
+    ANN101
+    ANN102
 exclude =
     docs/source/*
+    tests/*
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 6e435bee..494ea937 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -27,3 +27,4 @@ repos:
       - id: flake8
         additional_dependencies:
           - flake8-docstrings
+          - flake8-annotations
diff --git a/benchmark/primaite_benchmark.py b/benchmark/primaite_benchmark.py
index ead5723b..9fec5711 100644
--- a/benchmark/primaite_benchmark.py
+++ b/benchmark/primaite_benchmark.py
@@ -41,7 +41,7 @@ _TRAINING_CONFIG_PATH = _BENCHMARK_ROOT / "config" / "benchmark_training_config.
 _LAY_DOWN_CONFIG_PATH = data_manipulation_config_path()
 
 
-def get_size(size_bytes: int):
+def get_size(size_bytes: int) -> str:
     """
     Scale bytes to its proper format.
 
@@ -84,7 +84,7 @@ def _get_system_info() -> Dict:
 
 def _build_benchmark_latex_report(
     benchmark_metadata_dict: Dict, this_version_plot_path: Path, all_version_plot_path: Path
-):
+) -> None:
     geometry_options = {"tmargin": "2.5cm", "rmargin": "2.5cm", "bmargin": "2.5cm", "lmargin": "2.5cm"}
     data = benchmark_metadata_dict
     primaite_version = data["primaite_version"]
@@ -186,7 +186,7 @@ class BenchmarkPrimaiteSession(PrimaiteSession):
         self,
         training_config_path: Union[str, Path],
         lay_down_config_path: Union[str, Path],
-    ):
+    ) -> None:
         super().__init__(training_config_path, lay_down_config_path)
         self.setup()
 
@@ -195,10 +195,11 @@ class BenchmarkPrimaiteSession(PrimaiteSession):
         """Direct access to the env for ease of testing."""
         return self._agent_session._env  # noqa
 
-    def __enter__(self):
+    def __enter__(self) -> "BenchmarkPrimaiteSession":
         return self
 
-    def __exit__(self, type, value, tb):
+    # TODO: typehints uncertain
+    def __exit__(self, type: Any, value: Any, tb: Any) -> None:
         shutil.rmtree(self.session_path)
         _LOGGER.debug(f"Deleted benchmark session directory: {self.session_path}")
 
@@ -285,7 +286,7 @@ def _build_benchmark_results_dict(start_datetime: datetime, metadata_dict: Dict)
     return averaged_data
 
 
-def _get_df_from_episode_av_reward_dict(data: Dict):
+def _get_df_from_episode_av_reward_dict(data: Dict) -> pl.DataFrame:
     data: Dict = {"episode": data.keys(), "av_reward": data.values()}
 
     return (
@@ -360,7 +361,7 @@ def _plot_benchmark_metadata(
     return fig
 
 
-def _plot_all_benchmarks_combined_session_av():
+def _plot_all_benchmarks_combined_session_av() -> Figure:
     """
     Plot the Benchmark results for each released version of PrimAITE.
 
@@ -410,7 +411,7 @@ def _plot_all_benchmarks_combined_session_av():
     return fig
 
 
-def run():
+def run() -> None:
     """Run the PrimAITE benchmark."""
     start_datetime = datetime.now()
     av_reward_per_episode_dicts = {}
diff --git a/pyproject.toml b/pyproject.toml
index 4e8250d8..4982dfd1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -54,6 +54,7 @@ license-files = ["LICENSE"]
 dev = [
     "build==0.10.0",
     "flake8==6.0.0",
+    "flake8-annotations",
     "furo==2023.3.27",
     "gputil==1.4.0",
     "pip-licenses==4.3.0",
diff --git a/src/primaite/__init__.py b/src/primaite/__init__.py
index a0f5b7fe..ad157c9c 100644
--- a/src/primaite/__init__.py
+++ b/src/primaite/__init__.py
@@ -24,14 +24,14 @@ class _PrimaitePaths:
     The PlatformDirs appname is 'primaite' and the version is ``primaite.__version__`.
     """
 
-    def __init__(self):
+    def __init__(self) -> None:
         self._dirs: Final[PlatformDirs] = PlatformDirs(appname="primaite", version=__version__)
 
     def _get_dirs_properties(self) -> List[str]:
         class_items = self.__class__.__dict__.items()
         return [k for k, v in class_items if isinstance(v, property)]
 
-    def mkdirs(self):
+    def mkdirs(self) -> None:
         """
         Creates all Primaite directories.
 
@@ -102,7 +102,7 @@ class _PrimaitePaths:
         """The PrimAITE app log file path."""
         return self.app_log_dir_path / "primaite.log"
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         properties_str = ", ".join([f"{p}='{getattr(self, p)}'" for p in self._get_dirs_properties()])
         return f"{self.__class__.__name__}({properties_str})"
 
@@ -110,7 +110,7 @@ class _PrimaitePaths:
 PRIMAITE_PATHS: Final[_PrimaitePaths] = _PrimaitePaths()
 
 
-def _host_primaite_config():
+def _host_primaite_config() -> None:
     if not PRIMAITE_PATHS.app_config_file_path.exists():
         pkg_config_path = Path(pkg_resources.resource_filename("primaite", "setup/_package_data/primaite_config.yaml"))
         shutil.copy2(pkg_config_path, PRIMAITE_PATHS.app_config_file_path)
diff --git a/src/primaite/environment/observations.py b/src/primaite/environment/observations.py
index 383a9b5a..be80374b 100644
--- a/src/primaite/environment/observations.py
+++ b/src/primaite/environment/observations.py
@@ -443,7 +443,7 @@ class AccessControlList(AbstractObservationComponent):
 
     _DATA_TYPE: type = np.int64
 
-    def __init__(self, env: "Primaite"):
+    def __init__(self, env: "Primaite") -> None:
         """
         Initialise an AccessControlList observation component.