diff --git a/pandas/core/apply.py b/pandas/core/apply.py
index 2c96f1ef020ac..e228d20b359c6 100644
--- a/pandas/core/apply.py
+++ b/pandas/core/apply.py
@@ -10,6 +10,7 @@
     TYPE_CHECKING,
     Any,
     Literal,
+    TypeAlias,
     cast,
 )
 
@@ -71,7 +72,7 @@
     from pandas.core.resample import Resampler
     from pandas.core.window.rolling import BaseWindow
 
-ResType = dict[int, Any]
+ResType: TypeAlias = dict[int, Any]
 
 
 class BaseExecutionEngine(abc.ABC):
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 994d7b1d0081c..9a723a88941b6 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -10,6 +10,7 @@
     TYPE_CHECKING,
     Any,
     Literal,
+    TypeAlias,
     Union,
     cast,
     final,
@@ -161,7 +162,7 @@
         TimedeltaArray,
     )
 
-DTScalarOrNaT = Union[DatetimeLikeScalar, NaTType]
+DTScalarOrNaT: TypeAlias = DatetimeLikeScalar | NaTType
 
 
 def _make_unpacked_invalid_op(op_name: str):
@@ -386,7 +387,7 @@ def __getitem__(self, key: PositionalIndexer2D) -> Self | DTScalarOrNaT:
         # Use cast as we know we will get back a DatetimeLikeArray or DTScalar,
         # but skip evaluating the Union at runtime for performance
         # (see https://github.com/pandas-dev/pandas/pull/44624)
-        result = cast("Union[Self, DTScalarOrNaT]", super().__getitem__(key))
+        result = cast(Union[Self, DTScalarOrNaT], super().__getitem__(key))
         if lib.is_scalar(result):
             return result
         else:
diff --git a/pandas/core/arrays/interval.py b/pandas/core/arrays/interval.py
index 6cb79e915c78b..4bcbe2eedee47 100644
--- a/pandas/core/arrays/interval.py
+++ b/pandas/core/arrays/interval.py
@@ -9,7 +9,7 @@
 from typing import (
     TYPE_CHECKING,
     Literal,
-    Union,
+    TypeAlias,
     overload,
 )
 
@@ -109,8 +109,8 @@
     )
 
 
-IntervalSide = Union[TimeArrayLike, np.ndarray]
-IntervalOrNA = Union[Interval, float]
+IntervalSide: TypeAlias = TimeArrayLike | np.ndarray
+IntervalOrNA: TypeAlias = Interval | float
 
 _interval_shared_docs: dict[str, str] = {}
 
diff --git a/pandas/core/arrays/string_arrow.py b/pandas/core/arrays/string_arrow.py
index 9668981df827b..7264efa3298d9 100644
--- a/pandas/core/arrays/string_arrow.py
+++ b/pandas/core/arrays/string_arrow.py
@@ -4,7 +4,6 @@
 import re
 from typing import (
     TYPE_CHECKING,
-    Union,
 )
 import warnings
 
@@ -63,9 +62,6 @@
     from pandas import Series
 
 
-ArrowStringScalarOrNAT = Union[str, libmissing.NAType]
-
-
 def _chk_pyarrow_available() -> None:
     if pa_version_under10p1:
         msg = "pyarrow>=10.0.1 is required for PyArrow backed ArrowExtensionArray."
diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 49b80337c700e..b2531e2abf7f1 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -17,8 +17,8 @@
     Any,
     Literal,
     NamedTuple,
+    TypeAlias,
     TypeVar,
-    Union,
     cast,
 )
 import warnings
@@ -102,7 +102,7 @@
     from pandas.core.generic import NDFrame
 
 # TODO(typing) the return value on this callable should be any *scalar*.
-AggScalar = Union[str, Callable[..., Any]]
+AggScalar: TypeAlias = str | Callable[..., Any]
 # TODO: validate types on ScalarResult and move to _typing
 # Blocked from using by https://github.com/python/mypy/issues/1484
 # See note at _mangle_lambda_list
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 3daee98371844..f29423ce5e77c 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -26,6 +26,7 @@ class providing the base-class of operations.
 from typing import (
     TYPE_CHECKING,
     Literal,
+    TypeAlias,
     TypeVar,
     Union,
     cast,
@@ -449,13 +450,13 @@ def f(self):
         return attr
 
 
-_KeysArgType = Union[
-    Hashable,
-    list[Hashable],
-    Callable[[Hashable], Hashable],
-    list[Callable[[Hashable], Hashable]],
-    Mapping[Hashable, Hashable],
-]
+_KeysArgType: TypeAlias = (
+    Hashable
+    | list[Hashable]
+    | Callable[[Hashable], Hashable]
+    | list[Callable[[Hashable], Hashable]]
+    | Mapping[Hashable, Hashable]
+)
 
 
 class BaseGroupBy(PandasObject, SelectionMixin[NDFrameT], GroupByIndexingMixin):
@@ -957,9 +958,8 @@ def __iter__(self) -> Iterator[tuple[Hashable, NDFrameT]]:
         level = self.level
         result = self._grouper.get_iterator(self._selected_obj)
         # mypy: Argument 1 to "len" has incompatible type "Hashable"; expected "Sized"
-        if (
-            (is_list_like(level) and len(level) == 1)  # type: ignore[arg-type]
-            or (isinstance(keys, list) and len(keys) == 1)
+        if (is_list_like(level) and len(level) == 1) or (  # type: ignore[arg-type]
+            isinstance(keys, list) and len(keys) == 1
         ):
             # GH#42795 - when keys is a list, return tuples even when length is 1
             result = (((key,), group) for key, group in result)
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 34a437ba40bd8..994dcd4618a1c 100644
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -5,7 +5,6 @@
 from typing import (
     TYPE_CHECKING,
     Any,
-    TypeVar,
     cast,
     final,
 )
@@ -83,6 +82,7 @@
         Axis,
         AxisInt,
         Self,
+        T,
         npt,
     )
 
@@ -91,7 +91,6 @@
         Series,
     )
 
-T = TypeVar("T")
 # "null slice"
 _NS = slice(None, None)
 _one_ellipsis_message = "indexer may only contain one '...' entry"
diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index 0a10001a3113f..1b236deff330d 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -6,6 +6,7 @@
 from itertools import islice
 from typing import (
     TYPE_CHECKING,
+    TypeAlias,
     TypedDict,
     Union,
     cast,
@@ -93,13 +94,12 @@
 # ---------------------------------------------------------------------
 # types used in annotations
 
-ArrayConvertible = Union[list, tuple, AnyArrayLike]
-Scalar = Union[float, str]
-DatetimeScalar = Union[Scalar, date, np.datetime64]
+ArrayConvertible: TypeAlias = list | tuple | AnyArrayLike
+Scalar: TypeAlias = float | str
+DatetimeScalar: TypeAlias = Scalar | date | np.datetime64
 
-DatetimeScalarOrArrayConvertible = Union[DatetimeScalar, ArrayConvertible]
-
-DatetimeDictArg = Union[list[Scalar], tuple[Scalar, ...], AnyArrayLike]
+DatetimeScalarOrArrayConvertible: TypeAlias = DatetimeScalar | ArrayConvertible
+DatetimeDictArg: TypeAlias = list[Scalar] | tuple[Scalar, ...] | AnyArrayLike
 
 
 class YearMonthDayDict(TypedDict, total=True):
diff --git a/pandas/io/excel/_calamine.py b/pandas/io/excel/_calamine.py
index b8994e679d4b1..0bdd2b42aad51 100644
--- a/pandas/io/excel/_calamine.py
+++ b/pandas/io/excel/_calamine.py
@@ -9,7 +9,7 @@
 from typing import (
     TYPE_CHECKING,
     Any,
-    Union,
+    TypeAlias,
 )
 
 from pandas.compat._optional import import_optional_dependency
@@ -34,7 +34,7 @@
         StorageOptions,
     )
 
-_CellValue = Union[int, float, str, bool, time, date, datetime, timedelta]
+_CellValue: TypeAlias = int | float | str | bool | time | date | datetime | timedelta
 
 
 class CalamineReader(BaseExcelReader["CalamineWorkbook"]):
diff --git a/pandas/io/formats/printing.py b/pandas/io/formats/printing.py
index ab27321ffe83c..9de5ac071495b 100644
--- a/pandas/io/formats/printing.py
+++ b/pandas/io/formats/printing.py
@@ -14,8 +14,8 @@
 from typing import (
     TYPE_CHECKING,
     Any,
+    TypeAlias,
     TypeVar,
-    Union,
 )
 from unicodedata import east_asian_width
 
@@ -27,7 +27,7 @@
 
 if TYPE_CHECKING:
     from pandas._typing import ListLike
-EscapeChars = Union[Mapping[str, str], Iterable[str]]
+EscapeChars: TypeAlias = Mapping[str, str] | Iterable[str]
 _KT = TypeVar("_KT")
 _VT = TypeVar("_VT")
 
diff --git a/pandas/io/formats/style_render.py b/pandas/io/formats/style_render.py
index 6752c83d5169b..0747e7c84e1b0 100644
--- a/pandas/io/formats/style_render.py
+++ b/pandas/io/formats/style_render.py
@@ -11,9 +11,8 @@
     TYPE_CHECKING,
     Any,
     DefaultDict,
-    Optional,
+    TypeAlias,
     TypedDict,
-    Union,
 )
 from uuid import uuid4
 
@@ -50,11 +49,11 @@
 jinja2 = import_optional_dependency("jinja2", extra="DataFrame.style requires jinja2.")
 from markupsafe import escape as escape_html  # markupsafe is jinja2 dependency
 
-BaseFormatter = Union[str, Callable]
-ExtFormatter = Union[BaseFormatter, dict[Any, Optional[BaseFormatter]]]
-CSSPair = tuple[str, Union[str, float]]
-CSSList = list[CSSPair]
-CSSProperties = Union[str, CSSList]
+BaseFormatter: TypeAlias = str | Callable
+ExtFormatter: TypeAlias = BaseFormatter | dict[Any, BaseFormatter | None]
+CSSPair: TypeAlias = tuple[str, str | float]
+CSSList: TypeAlias = list[CSSPair]
+CSSProperties: TypeAlias = str | CSSList
 
 
 class CSSDict(TypedDict):
@@ -62,8 +61,8 @@ class CSSDict(TypedDict):
     props: CSSProperties
 
 
-CSSStyles = list[CSSDict]
-Subset = Union[slice, Sequence, Index]
+CSSStyles: TypeAlias = list[CSSDict]
+Subset = slice | Sequence | Index
 
 
 class StylerRenderer:
diff --git a/pandas/io/pytables.py b/pandas/io/pytables.py
index c58b4a4be6df1..64a05c87e0f80 100644
--- a/pandas/io/pytables.py
+++ b/pandas/io/pytables.py
@@ -20,6 +20,7 @@
     Any,
     Final,
     Literal,
+    TypeAlias,
     cast,
     overload,
 )
@@ -160,7 +161,7 @@ def _ensure_str(name):
     return name
 
 
-Term = PyTablesExpr
+Term: TypeAlias = PyTablesExpr
 
 
 def _ensure_term(where, scope_level: int):
diff --git a/pandas/tests/io/pytables/test_errors.py b/pandas/tests/io/pytables/test_errors.py
index b28101c09820f..23932b6092998 100644
--- a/pandas/tests/io/pytables/test_errors.py
+++ b/pandas/tests/io/pytables/test_errors.py
@@ -45,7 +45,7 @@ def test_pass_spec_to_storer(setup_path):
             "format store. this store must be selected in its entirety"
         )
         with pytest.raises(TypeError, match=msg):
-            store.select("df", where=[("columns=A")])
+            store.select("df", where=["columns=A"])
 
 
 def test_table_index_incompatible_dtypes(setup_path):
diff --git a/pandas/tests/io/pytables/test_select.py b/pandas/tests/io/pytables/test_select.py
index 5e76aae28c147..0dffb284fa6d2 100644
--- a/pandas/tests/io/pytables/test_select.py
+++ b/pandas/tests/io/pytables/test_select.py
@@ -143,7 +143,7 @@ def test_select(setup_path):
         tm.assert_frame_equal(expected, result)
 
         # equivalently
-        result = store.select("df", [("columns=['A', 'B']")])
+        result = store.select("df", ["columns=['A', 'B']"])
         expected = df.reindex(columns=["A", "B"])
         tm.assert_frame_equal(expected, result)
 
diff --git a/pandas/util/version/__init__.py b/pandas/util/version/__init__.py
index bd741140f6542..15696c9292eda 100644
--- a/pandas/util/version/__init__.py
+++ b/pandas/util/version/__init__.py
@@ -13,7 +13,7 @@
     Any,
     NamedTuple,
     SupportsInt,
-    Union,
+    TypeAlias,
 )
 
 __all__ = ["VERSION_PATTERN", "InvalidVersion", "Version", "parse"]
@@ -77,14 +77,14 @@ def __neg__(self: object) -> InfinityType:
 NegativeInfinity = NegativeInfinityType()
 
 
-LocalType = tuple[Union[int, str], ...]
+LocalType: TypeAlias = tuple[int | str, ...]
 
-CmpPrePostDevType = Union[InfinityType, NegativeInfinityType, tuple[str, int]]
-CmpLocalType = Union[
-    NegativeInfinityType,
-    tuple[Union[tuple[int, str], tuple[NegativeInfinityType, Union[int, str]]], ...],
-]
-CmpKey = tuple[
+CmpPrePostDevType: TypeAlias = InfinityType | NegativeInfinityType | tuple[str, int]
+CmpLocalType: TypeAlias = (
+    NegativeInfinityType
+    | tuple[tuple[int, str] | tuple[NegativeInfinityType, int | str], ...]
+)
+CmpKey: TypeAlias = tuple[
     int,
     tuple[int, ...],
     CmpPrePostDevType,
@@ -92,7 +92,7 @@ def __neg__(self: object) -> InfinityType:
     CmpPrePostDevType,
     CmpLocalType,
 ]
-VersionComparisonMethod = Callable[[CmpKey, CmpKey], bool]
+VersionComparisonMethod: TypeAlias = Callable[[CmpKey, CmpKey], bool]
 
 
 class _Version(NamedTuple):