diff --git a/pint/facets/context/objects.py b/pint/facets/context/objects.py
index edd1dfb2a..3e9e56d06 100644
--- a/pint/facets/context/objects.py
+++ b/pint/facets/context/objects.py
@@ -240,7 +240,7 @@ def redefine(self, definition: str) -> None:
             if isinstance(definition, UnitDefinition):
                 self._redefine(definition)
 
-    def _redefine(self, definition: UnitDefinition):
+    def _redefine(self, definition: UnitDefinition) -> None:
         self.redefinitions.append(definition)
 
     def hashable(
@@ -274,13 +274,13 @@ class ContextChain(ChainMap[SrcDst, Context]):
     to transform from one dimension to another.
     """
 
-    def __init__(self):
+    def __init__(self) -> None:
         super().__init__()
         self.contexts: list[Context] = []
         self.maps.clear()  # Remove default empty map
         self._graph: dict[SrcDst, set[UnitsContainer]] | None = None
 
-    def insert_contexts(self, *contexts: Context):
+    def insert_contexts(self, *contexts: Context) -> None:
         """Insert one or more contexts in reversed order the chained map.
         (A rule in last context will take precedence)
 
@@ -292,7 +292,7 @@ def insert_contexts(self, *contexts: Context):
         self.maps = [ctx.relation_to_context for ctx in reversed(contexts)] + self.maps
         self._graph = None
 
-    def remove_contexts(self, n: int | None = None):
+    def remove_contexts(self, n: int | None = None) -> None:
         """Remove the last n inserted contexts from the chain.
 
         Parameters
diff --git a/pint/facets/dask/__init__.py b/pint/facets/dask/__init__.py
index c3133bc31..91e0b5ee1 100644
--- a/pint/facets/dask/__init__.py
+++ b/pint/facets/dask/__init__.py
@@ -110,7 +110,7 @@ def persist(self, **kwargs):
         return result
 
     @check_dask_array
-    def visualize(self, **kwargs):
+    def visualize(self, **kwargs) -> None:
         """Produce a visual representation of the Dask graph.
 
         The graphviz library is required.
diff --git a/pint/facets/group/objects.py b/pint/facets/group/objects.py
index 751dd3765..5c82aca41 100644
--- a/pint/facets/group/objects.py
+++ b/pint/facets/group/objects.py
@@ -58,7 +58,7 @@ class Group(SharedRegistryObject):
         If not given, a root Group will be created.
     """
 
-    def __init__(self, name: str):
+    def __init__(self, name: str) -> None:
         # The name of the group.
         self.name = name
 
diff --git a/pint/facets/group/registry.py b/pint/facets/group/registry.py
index 33f78c645..cb72753cc 100644
--- a/pint/facets/group/registry.py
+++ b/pint/facets/group/registry.py
@@ -44,7 +44,7 @@ class GenericGroupRegistry(
     # to enjoy typing goodies
     Group = type[objects.Group]
 
-    def __init__(self, **kwargs):
+    def __init__(self, **kwargs) -> None:
         super().__init__(**kwargs)
         #: Map group name to group.
         self._groups: dict[str, objects.Group] = {}
@@ -81,7 +81,7 @@ def _register_definition_adders(self) -> None:
         super()._register_definition_adders()
         self._register_adder(GroupDefinition, self._add_group)
 
-    def _add_unit(self, definition: UnitDefinition):
+    def _add_unit(self, definition: UnitDefinition) -> None:
         super()._add_unit(definition)
         # TODO: delta units are missing
         self.get_group("root").add_units(definition.name)
diff --git a/pint/facets/numpy/numpy_func.py b/pint/facets/numpy/numpy_func.py
index b79700f9f..fd27c5e1c 100644
--- a/pint/facets/numpy/numpy_func.py
+++ b/pint/facets/numpy/numpy_func.py
@@ -247,7 +247,7 @@ def decorator(func):
     return decorator
 
 
-def implement_func(func_type, func_str, input_units=None, output_unit=None):
+def implement_func(func_type, func_str, input_units=None, output_unit=None) -> None:
     """Add default-behavior NumPy function/ufunc to the handled list.
 
     Parameters
@@ -597,7 +597,7 @@ def _unwrap(p, discont=None, axis=-1):
 
 
 @implements("copyto", "function")
-def _copyto(dst, src, casting="same_kind", where=True):
+def _copyto(dst, src, casting="same_kind", where=True) -> None:
     if _is_quantity(dst):
         if _is_quantity(src):
             src = src.m_as(dst.units)
@@ -700,7 +700,7 @@ def _all(a, *args, **kwargs):
         raise ValueError("Boolean value of Quantity with offset unit is ambiguous.")
 
 
-def implement_prod_func(name):
+def implement_prod_func(name) -> None:
     if np is None:
         return
 
@@ -788,7 +788,7 @@ def _correlate(a, v, mode="valid", **kwargs):
     return a.units._REGISTRY.Quantity(ret, units)
 
 
-def implement_mul_func(func):
+def implement_mul_func(func) -> None:
     # If NumPy is not available, do not attempt implement that which does not exist
     if np is None:
         return
@@ -815,7 +815,7 @@ def implementation(a, b, **kwargs):
 # Implement simple matching-unit or stripped-unit functions based on signature
 
 
-def implement_consistent_units_by_argument(func_str, unit_arguments, wrap_output=True):
+def implement_consistent_units_by_argument(func_str, unit_arguments, wrap_output=True) -> None:
     # If NumPy is not available, do not attempt implement that which does not exist
     if np is None:
         return
@@ -916,7 +916,7 @@ def implementation(*args, **kwargs):
 
 
 # implement isclose and allclose
-def implement_close(func_str):
+def implement_close(func_str) -> None:
     if np is None:
         return
 
@@ -950,7 +950,7 @@ def implementation(*args, **kwargs):
 # Handle atleast_nd functions
 
 
-def implement_atleast_nd(func_str):
+def implement_atleast_nd(func_str) -> None:
     # If NumPy is not available, do not attempt implement that which does not exist
     if np is None:
         return
@@ -979,7 +979,7 @@ def implementation(*arrays):
 
 # Handle cumulative products (which must be dimensionless for consistent units across
 # output array)
-def implement_single_dimensionless_argument_func(func_str):
+def implement_single_dimensionless_argument_func(func_str) -> None:
     # If NumPy is not available, do not attempt implement that which does not exist
     if np is None:
         return
diff --git a/pint/facets/numpy/quantity.py b/pint/facets/numpy/quantity.py
index 75dccec54..f1d56b478 100644
--- a/pint/facets/numpy/quantity.py
+++ b/pint/facets/numpy/quantity.py
@@ -179,7 +179,7 @@ def dtype(self):
         return self._magnitude.dtype
 
     @shape.setter
-    def shape(self, value):
+    def shape(self, value) -> None:
         self._magnitude.shape = value
 
     def searchsorted(self, v, side="left", sorter=None):
@@ -207,7 +207,7 @@ def prod(self, *args, **kwargs):
         """
         return np.prod(self, *args, **kwargs)
 
-    def __ito_if_needed(self, to_units):
+    def __ito_if_needed(self, to_units) -> None:
         if self.unitless and to_units == "radian":
             return
 
diff --git a/pint/facets/plain/definitions.py b/pint/facets/plain/definitions.py
index a43ce0dbc..edf122149 100644
--- a/pint/facets/plain/definitions.py
+++ b/pint/facets/plain/definitions.py
@@ -24,7 +24,7 @@
 class NotNumeric(Exception):
     """Internal exception. Do not expose outside Pint"""
 
-    def __init__(self, value: Any):
+    def __init__(self, value: Any) -> None:
         self.value = value
 
 
diff --git a/pint/facets/plain/registry.py b/pint/facets/plain/registry.py
index be70a2ca8..f1fa16387 100644
--- a/pint/facets/plain/registry.py
+++ b/pint/facets/plain/registry.py
@@ -231,7 +231,7 @@ def __init__(
         cache_folder: str | pathlib.Path | None = None,
         separate_format_defaults: bool | None = None,
         mpl_formatter: str = "{:P}",
-    ):
+    ) -> None:
         #: Map a definition class to a adder methods.
         self._adders: Handler = {}
         self._register_definition_adders()
@@ -415,7 +415,7 @@ def fmt_locale(self) -> Locale | None:
         "This function will be removed in future versions of pint.\n"
         "Use ureg.formatter.set_locale"
     )
-    def fmt_locale(self, loc: str | None):
+    def fmt_locale(self, loc: str | None) -> None:
         self.formatter.set_locale(loc)
 
     @deprecated(
diff --git a/pint/facets/system/objects.py b/pint/facets/system/objects.py
index 751a66abf..b5367b3b3 100644
--- a/pint/facets/system/objects.py
+++ b/pint/facets/system/objects.py
@@ -54,7 +54,7 @@ class System(SharedRegistryObject):
         Name of the group.
     """
 
-    def __init__(self, name: str):
+    def __init__(self, name: str) -> None:
         #: Name of the system
         #: :type: str
         self.name = name
@@ -103,7 +103,7 @@ def members(self):
 
         return self._computed_members
 
-    def invalidate_members(self):
+    def invalidate_members(self) -> None:
         """Invalidate computed members in this Group and all parent nodes."""
         self._computed_members = None
 
@@ -205,7 +205,7 @@ def from_definition(
 
 
 class Lister:
-    def __init__(self, d: dict[str, Any]):
+    def __init__(self, d: dict[str, Any]) -> None:
         self.d = d
 
     def __dir__(self) -> list[str]:
diff --git a/pint/facets/system/registry.py b/pint/facets/system/registry.py
index e5235a4cb..c614348e5 100644
--- a/pint/facets/system/registry.py
+++ b/pint/facets/system/registry.py
@@ -51,7 +51,7 @@ class GenericSystemRegistry(
     # to enjoy typing goodies
     System: type[objects.System]
 
-    def __init__(self, system: str | None = None, **kwargs):
+    def __init__(self, system: str | None = None, **kwargs) -> None:
         super().__init__(**kwargs)
 
         #: Map system name to system.
diff --git a/pyproject.toml b/pyproject.toml
index 9f29f8f92..819ed717a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -104,3 +104,18 @@ ignore = [
   # line break before binary operator
   # "W503"
 ]
+
+# Configuration for mypy
+# https://mypy.readthedocs.io/en/stable/config_file.html#using-a-pyproject-toml-file
+[tool.mypy]
+# python_version = "3.9"
+# follow_imports = "skip"
+ignore_missing_imports = true
+files = "pint/facets"  # directory mypy should analyze
+# # Directories to exclude from mypy's analysis
+# exclude = [
+#     "pint/testsuite",
+#     "docs",
+#     "pint/default_en.txt",
+#     "pint/constants_en.txt",
+# ]
\ No newline at end of file