diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92b8333..437ce3b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 - Changed
   - Dropped support for Python 3.8
+  - Use "modern" type annotation, such as `list` and `str | None`
 - Added
   - Added static type checking using `mypy`
 
diff --git a/pydoclint/baseline.py b/pydoclint/baseline.py
index 427d0d5..a0b375a 100644
--- a/pydoclint/baseline.py
+++ b/pydoclint/baseline.py
@@ -1,6 +1,7 @@
+from __future__ import annotations
+
 from itertools import groupby
 from pathlib import Path
-from typing import Dict, List, Set, Tuple
 
 from pydoclint.utils.violation import Violation
 
@@ -10,7 +11,7 @@
 
 
 def generateBaseline(
-        violationsInAllFiles: Dict[str, List[Violation]], path: Path
+        violationsInAllFiles: dict[str, list[Violation]], path: Path
 ) -> None:
     """Generate baseline file based of passed violations."""
     with path.open('w', encoding='utf-8') as baseline:
@@ -23,7 +24,7 @@ def generateBaseline(
                 baseline.write(f'{SEPARATOR}')
 
 
-def parseBaseline(path: Path) -> Dict[str, Set[str]]:
+def parseBaseline(path: Path) -> dict[str, set[str]]:
     """Parse baseline file."""
     with path.open('r', encoding='utf-8') as baseline:
         parsed: dict[str, set[str]] = {}
@@ -41,15 +42,15 @@ def parseBaseline(path: Path) -> Dict[str, Set[str]]:
 
 
 def removeBaselineViolations(
-        baseline: Dict[str, Set[str]],
-        violationsInAllFiles: Dict[str, List[Violation]],
-) -> Tuple[bool, Dict[str, List[Violation]]]:
+        baseline: dict[str, set[str]],
+        violationsInAllFiles: dict[str, list[Violation]],
+) -> tuple[bool, dict[str, list[Violation]]]:
     """
     Remove from the violation dictionary the already existing violations
     specified in the baseline file.
     """
     baselineRegenerationNeeded = False
-    clearedViolationsAllFiles: Dict[str, List[Violation]] = {}
+    clearedViolationsAllFiles: dict[str, list[Violation]] = {}
     for file, violations in violationsInAllFiles.items():
         if oldViolations := baseline.get(file):
             newViolations = []
diff --git a/pydoclint/flake8_entry.py b/pydoclint/flake8_entry.py
index 74558f2..cab2f1a 100644
--- a/pydoclint/flake8_entry.py
+++ b/pydoclint/flake8_entry.py
@@ -1,8 +1,9 @@
 # mypy: disable-error-code=attr-defined
+from __future__ import annotations
 
 import ast
 import importlib.metadata as importlib_metadata
-from typing import Any, Generator, Tuple
+from typing import Any, Generator
 
 from pydoclint.visitor import Visitor
 
@@ -230,7 +231,7 @@ def parse_options(cls, options: Any) -> None:  # noqa: D102
         )
         cls.style = options.style
 
-    def run(self) -> Generator[Tuple[int, int, str, Any], None, None]:
+    def run(self) -> Generator[tuple[int, int, str, Any], None, None]:
         """Run the linter and yield the violation information"""
         if self.type_hints_in_docstring != 'None':  # user supplies this option
             raise ValueError(
diff --git a/pydoclint/main.py b/pydoclint/main.py
index 7a0b8d5..04dbc55 100644
--- a/pydoclint/main.py
+++ b/pydoclint/main.py
@@ -1,8 +1,9 @@
+from __future__ import annotations
+
 import ast
 import logging
 import re
 from pathlib import Path
-from typing import Dict, List, Optional, Tuple
 
 import click
 
@@ -28,8 +29,8 @@
 def validateStyleValue(
         context: click.Context,
         param: click.Parameter,
-        value: Optional[str],
-) -> Optional[str]:
+        value: str | None,
+) -> str | None:
     """Validate the value of the 'style' option"""
     if value not in {'numpy', 'google', 'sphinx'}:
         raise click.BadParameter(
@@ -306,7 +307,7 @@ def main(  # noqa: C901
         quiet: bool,
         exclude: str,
         style: str,
-        paths: Tuple[str, ...],
+        paths: tuple[str, ...],
         type_hints_in_signature: str,
         type_hints_in_docstring: str,
         arg_type_hints_in_signature: bool,
@@ -327,7 +328,7 @@ def main(  # noqa: C901
         generate_baseline: bool,
         baseline: str,
         show_filenames_in_every_violation_message: bool,
-        config: Optional[str],  # don't remove it b/c it's required by `click`
+        config: str | None,  # don't remove it b/c it's required by `click`
 ) -> None:
     """Command-line entry point of pydoclint"""
     logging.basicConfig(level=logging.WARN if quiet else logging.INFO)
@@ -392,7 +393,7 @@ def main(  # noqa: C901
             )
             ctx.exit(1)
 
-    violationsInAllFiles: Dict[str, List[Violation]] = _checkPaths(
+    violationsInAllFiles: dict[str, list[Violation]] = _checkPaths(
         quiet=quiet,
         exclude=exclude,
         style=style,
@@ -516,7 +517,7 @@ def main(  # noqa: C901
 
 
 def _checkPaths(
-        paths: Tuple[str, ...],
+        paths: tuple[str, ...],
         style: str = 'numpy',
         argTypeHintsInSignature: bool = True,
         argTypeHintsInDocstring: bool = True,
@@ -534,8 +535,8 @@ def _checkPaths(
         requireYieldSectionWhenYieldingNothing: bool = False,
         quiet: bool = False,
         exclude: str = '',
-) -> Dict[str, List[Violation]]:
-    filenames: List[Path] = []
+) -> dict[str, list[Violation]]:
+    filenames: list[Path] = []
 
     if not quiet:
         skipMsg = f'Skipping files that match this pattern: {exclude}'
@@ -552,7 +553,7 @@ def _checkPaths(
         elif path.is_dir():
             filenames.extend(sorted(path.rglob('*.py')))
 
-    allViolations: Dict[str, List[Violation]] = {}
+    allViolations: dict[str, list[Violation]] = {}
 
     for filename in filenames:
         if excludePattern.search(filename.as_posix()):
@@ -563,7 +564,7 @@ def _checkPaths(
                 click.style(filename, fg='cyan', bold=True), err=echoAsError
             )
 
-        violationsInThisFile: List[Violation] = _checkFile(
+        violationsInThisFile: list[Violation] = _checkFile(
             filename,
             style=style,
             argTypeHintsInSignature=argTypeHintsInSignature,
@@ -611,7 +612,7 @@ def _checkFile(
         treatPropertyMethodsAsClassAttributes: bool = False,
         requireReturnSectionWhenReturningNothing: bool = False,
         requireYieldSectionWhenYieldingNothing: bool = False,
-) -> List[Violation]:
+) -> list[Violation]:
     if not filename.is_file():  # sometimes folder names can end with `.py`
         return []
 
diff --git a/pydoclint/parse_config.py b/pydoclint/parse_config.py
index 25c4847..1a099b0 100644
--- a/pydoclint/parse_config.py
+++ b/pydoclint/parse_config.py
@@ -1,7 +1,9 @@
+from __future__ import annotations
+
 import logging
 import sys
 from pathlib import Path
-from typing import Any, Dict, Optional, Sequence
+from typing import Any, Sequence
 
 import click
 
@@ -14,8 +16,8 @@
 def injectDefaultOptionsFromUserSpecifiedTomlFilePath(
         ctx: click.Context,
         param: click.Parameter,
-        value: Optional[str],
-) -> Optional[str]:
+        value: str | None,
+) -> str | None:
     """
     Inject default objects from user-specified .toml file path.
 
@@ -25,13 +27,13 @@ def injectDefaultOptionsFromUserSpecifiedTomlFilePath(
         The "click" context
     param : click.Parameter
         The "click" parameter; not used in this function; just a placeholder
-    value : Optional[str]
+    value : str | None
         The full path of the .toml file. (It needs to be named ``value``
         so that ``click`` can correctly use it as a callback function.)
 
     Returns
     -------
-    Optional[str]
+    str | None
         The full path of the .toml file
     """
     if not value:
@@ -43,7 +45,7 @@ def injectDefaultOptionsFromUserSpecifiedTomlFilePath(
     return value
 
 
-def parseToml(paths: Optional[Sequence[str]]) -> Dict[str, Any]:
+def parseToml(paths: Sequence[str] | None) -> dict[str, Any]:
     """Parse the pyproject.toml located in the common parent of ``paths``"""
     if paths is None:
         return {}
@@ -56,7 +58,7 @@ def parseToml(paths: Optional[Sequence[str]]) -> Dict[str, Any]:
     return parseOneTomlFile(tomlFilename)
 
 
-def parseOneTomlFile(tomlFilename: Path) -> Dict[str, Any]:
+def parseOneTomlFile(tomlFilename: Path) -> dict[str, Any]:
     """Parse a .toml file"""
     if not tomlFilename.exists():
         logging.info(f'File "{tomlFilename}" does not exist; nothing to load.')
@@ -105,9 +107,9 @@ def findCommonParentFolder(
     return common_parent
 
 
-def updateCtxDefaultMap(ctx: click.Context, config: Dict[str, Any]) -> None:
+def updateCtxDefaultMap(ctx: click.Context, config: dict[str, Any]) -> None:
     """Update the ``click`` context default map with the provided ``config``"""
-    default_map: Dict[str, Any] = {}
+    default_map: dict[str, Any] = {}
     if ctx.default_map:
         default_map.update(ctx.default_map)
 
diff --git a/pydoclint/utils/arg.py b/pydoclint/utils/arg.py
index 4b0e08e..165eb44 100644
--- a/pydoclint/utils/arg.py
+++ b/pydoclint/utils/arg.py
@@ -1,5 +1,6 @@
+from __future__ import annotations
+
 import ast
-from typing import List, Optional, Set
 
 from docstring_parser.common import DocstringAttr, DocstringParam
 
@@ -84,8 +85,8 @@ def fromDocstringAttr(cls, attr: DocstringAttr) -> 'Arg':
     @classmethod
     def fromAstArg(cls, astArg: ast.arg) -> 'Arg':
         """Construct an Arg object from a Python AST argument object"""
-        anno: Optional[ast.expr] = astArg.annotation
-        typeHint: Optional[str] = '' if anno is None else unparseName(anno)
+        anno: ast.expr | None = astArg.annotation
+        typeHint: str | None = '' if anno is None else unparseName(anno)
         assert typeHint is not None  # to help mypy better understand type
         return Arg(name=astArg.arg, typeHint=typeHint)
 
@@ -102,7 +103,7 @@ def fromAstAnnAssign(cls, astAnnAssign: ast.AnnAssign) -> 'Arg':
         return Arg(name=unparsedArgName, typeHint=unparsedTypeHint)
 
     @classmethod
-    def _str(cls, typeName: Optional[str]) -> str:
+    def _str(cls, typeName: str | None) -> str:
         return '' if typeName is None else typeName
 
     @classmethod
@@ -148,7 +149,7 @@ class ArgList:
     equality, length calculation, etc.
     """
 
-    def __init__(self, infoList: List[Arg]):
+    def __init__(self, infoList: list[Arg]) -> None:
         if not all(isinstance(_, Arg) for _ in infoList):
             raise TypeError('All elements of `infoList` must be Arg.')
 
@@ -186,7 +187,7 @@ def length(self) -> int:
         return len(self.infoList)
 
     @classmethod
-    def fromDocstringParam(cls, params: List[DocstringParam]) -> 'ArgList':
+    def fromDocstringParam(cls, params: list[DocstringParam]) -> 'ArgList':
         """Construct an ArgList from a list of DocstringParam objects"""
         infoList = [
             Arg.fromDocstringParam(_)
@@ -198,7 +199,7 @@ def fromDocstringParam(cls, params: List[DocstringParam]) -> 'ArgList':
     @classmethod
     def fromDocstringAttr(
             cls,
-            params: List[DocstringAttr],
+            params: list[DocstringAttr],
     ) -> 'ArgList':
         """Construct an ArgList from a list of DocstringAttr objects"""
         infoList = [
@@ -212,7 +213,7 @@ def fromDocstringAttr(
     @classmethod
     def fromAstAssign(cls, astAssign: ast.Assign) -> 'ArgList':
         """Construct an ArgList from variable declaration/assignment"""
-        infoList: List[Arg] = []
+        infoList: list[Arg] = []
         for i, target in enumerate(astAssign.targets):
             if isinstance(target, ast.Tuple):  # such as `a, b = c, d = 1, 2`
                 for j, item in enumerate(target.elts):
@@ -226,7 +227,7 @@ def fromAstAssign(cls, astAssign: ast.Assign) -> 'ArgList':
             elif isinstance(target, ast.Name):  # such as `a = 1` or `a = b = 2`
                 infoList.append(Arg(name=target.id, typeHint=''))
             elif isinstance(target, ast.Attribute):  # e.g., uvw.xyz = 1
-                unparsedTarget: Optional[str] = unparseName(target)
+                unparsedTarget: str | None = unparseName(target)
                 assert unparsedTarget is not None  # to help mypy understand type
                 infoList.append(Arg(name=unparsedTarget, typeHint=''))
             else:
@@ -295,13 +296,13 @@ def equals(
 
         return verdict  # noqa: R504
 
-    def findArgsWithDifferentTypeHints(self, other: 'ArgList') -> List[Arg]:
+    def findArgsWithDifferentTypeHints(self, other: 'ArgList') -> list[Arg]:
         """Find args with unmatched type hints."""
         if not self.equals(other, checkTypeHint=False, orderMatters=False):
             msg = 'These 2 arg lists do not have the same arg names'
             raise EdgeCaseError(msg)
 
-        result: List[Arg] = []
+        result: list[Arg] = []
         for selfArg in self.infoList:
             selfArgTypeHint: str = selfArg.typeHint
             otherArgTypeHint: str = other.lookup[selfArg.name]
@@ -314,7 +315,7 @@ def subtract(
             self,
             other: 'ArgList',
             checkTypeHint: bool = True,
-    ) -> Set[Arg]:
+    ) -> set[Arg]:
         """Find the args that are in this object but not in `other`."""
         if checkTypeHint:
             return set(self.infoList) - set(other.infoList)
diff --git a/pydoclint/utils/astTypes.py b/pydoclint/utils/astTypes.py
index 8e02f46..77a0a84 100644
--- a/pydoclint/utils/astTypes.py
+++ b/pydoclint/utils/astTypes.py
@@ -1,7 +1,11 @@
+from __future__ import annotations
+
 import ast
 import sys
 from typing import Union
 
+# typing.Union is still needed when defining custom types in Python 3.9.
+# It can be changed to `xxx | yyy` after Python 3.9 is dropped.
 FuncOrAsyncFuncDef = Union[ast.AsyncFunctionDef, ast.FunctionDef]
 ClassOrFunctionDef = Union[ast.ClassDef, ast.AsyncFunctionDef, ast.FunctionDef]
 
diff --git a/pydoclint/utils/doc.py b/pydoclint/utils/doc.py
index 720c1c0..50450fd 100644
--- a/pydoclint/utils/doc.py
+++ b/pydoclint/utils/doc.py
@@ -1,5 +1,7 @@
+from __future__ import annotations
+
 import pprint
-from typing import Any, List, Optional, Union
+from typing import Any
 
 from docstring_parser.common import (
     Docstring,
@@ -23,7 +25,7 @@ def __init__(self, docstring: str, style: str = 'numpy') -> None:
         self.docstring = docstring
         self.style = style
 
-        parser: Union[NumpydocParser, GoogleParser]
+        parser: NumpydocParser | GoogleParser
         if style == 'numpy':
             parser = NumpydocParser()
             self.parsed = parser.parse(docstring)
@@ -80,7 +82,7 @@ def attrList(self) -> ArgList:  # type:ignore[return]
     def hasReturnsSection(self) -> bool:  # type:ignore[return]
         """Whether the docstring has a 'Returns' section"""
         if self.style in {'google', 'numpy', 'sphinx'}:
-            retSection: Optional[DocstringReturns] = self.parsed.returns
+            retSection: DocstringReturns | None = self.parsed.returns
             return retSection is not None and not retSection.is_generator
 
         self._raiseException()  # noqa: R503
@@ -103,11 +105,11 @@ def hasRaisesSection(self) -> bool:  # type:ignore[return]
         self._raiseException()  # noqa: R503
 
     @property
-    def returnSection(self) -> List[ReturnArg]:
+    def returnSection(self) -> list[ReturnArg]:
         """Get the return section of the docstring"""
         if isinstance(self.parsed, Docstring):  # Google, numpy, Sphinx styles
-            returnSection: List[DocstringReturns] = self.parsed.many_returns
-            result: List[ReturnArg] = []
+            returnSection: list[DocstringReturns] = self.parsed.many_returns
+            result: list[ReturnArg] = []
             for element in returnSection:
                 result.append(
                     ReturnArg(
@@ -122,11 +124,11 @@ def returnSection(self) -> List[ReturnArg]:
         return []
 
     @property
-    def yieldSection(self) -> List[YieldArg]:
+    def yieldSection(self) -> list[YieldArg]:
         """Get the yield section of the docstring"""
         if isinstance(self.parsed, Docstring):  # Google, numpy, Sphinx styles
-            yieldSection: List[DocstringYields] = self.parsed.many_yields
-            result: List[YieldArg] = []
+            yieldSection: list[DocstringYields] = self.parsed.many_yields
+            result: list[YieldArg] = []
             for element in yieldSection:
                 result.append(
                     YieldArg(
diff --git a/pydoclint/utils/generic.py b/pydoclint/utils/generic.py
index 7560617..65e78d7 100644
--- a/pydoclint/utils/generic.py
+++ b/pydoclint/utils/generic.py
@@ -3,7 +3,7 @@
 import ast
 import copy
 import re
-from typing import TYPE_CHECKING, List, Match, Optional, Tuple, Union
+from typing import TYPE_CHECKING, Match
 
 from pydoclint.utils.astTypes import ClassOrFunctionDef, FuncOrAsyncFuncDef
 from pydoclint.utils.method_type import MethodType
@@ -13,12 +13,12 @@
     from pydoclint.utils.arg import Arg, ArgList
 
 
-def collectFuncArgs(node: FuncOrAsyncFuncDef) -> List[ast.arg]:
+def collectFuncArgs(node: FuncOrAsyncFuncDef) -> list[ast.arg]:
     """
     Collect all arguments from a function node, and return them in
     their original order in the function signature.
     """
-    allArgs: List[ast.arg] = []
+    allArgs: list[ast.arg] = []
     allArgs.extend(node.args.args)
     allArgs.extend(node.args.posonlyargs)
     allArgs.extend(node.args.kwonlyargs)
@@ -64,7 +64,7 @@ def collectFuncArgs(node: FuncOrAsyncFuncDef) -> List[ast.arg]:
     )
 
 
-def getFunctionId(node: FuncOrAsyncFuncDef) -> Tuple[int, int, str]:
+def getFunctionId(node: FuncOrAsyncFuncDef) -> tuple[int, int, str]:
     """
     Get unique identifier of a function def. We also need line and
     column number because different function can have identical names.
@@ -100,7 +100,7 @@ def detectMethodType(node: FuncOrAsyncFuncDef) -> MethodType:
 
 def getDocstring(node: ClassOrFunctionDef) -> str:
     """Get docstring from a class definition or a function definition"""
-    docstring_: Optional[str] = ast.get_docstring(node)
+    docstring_: str | None = ast.get_docstring(node)
     return '' if docstring_ is None else docstring_
 
 
@@ -167,10 +167,7 @@ def getNodeName(node: ast.AST) -> str:
     return getattr(node, 'name', '')
 
 
-def stringStartsWith(
-        string: Optional[str],
-        substrings: Tuple[str, ...],
-) -> bool:
+def stringStartsWith(string: str | None, substrings: tuple[str, ...]) -> bool:
     """Check whether the string starts with any of the substrings"""
     if string is None:
         return False
@@ -182,7 +179,7 @@ def stringStartsWith(
     return False
 
 
-def stripQuotes(string: Optional[str]) -> Optional[str]:
+def stripQuotes(string: str | None) -> str | None:
     """
     Strip quotes (both double and single quotes) from the given string.
     Also, strip backticks (`) or double backticks (``) from the beginning
@@ -217,7 +214,7 @@ def appendArgsToCheckToV105(
         docArgs: ArgList,
 ) -> Violation:
     """Append the arg names to check to the error message of v105 or v605"""
-    argsToCheck: List[Arg] = funcArgs.findArgsWithDifferentTypeHints(docArgs)
+    argsToCheck: list[Arg] = funcArgs.findArgsWithDifferentTypeHints(docArgs)
     argNames: str = ', '.join(_.name for _ in argsToCheck)
     return original_v105.appendMoreMsg(moreMsg=argNames)
 
@@ -250,7 +247,7 @@ def specialEqual(str1: str, str2: str) -> bool:
     return True
 
 
-def getFullAttributeName(node: Union[ast.Attribute, ast.Name]) -> str:
+def getFullAttributeName(node: ast.Attribute | ast.Name) -> str:
     """Get the full name of a symbol like a.b.c.foo"""
     if isinstance(node, ast.Name):
         return node.id
diff --git a/pydoclint/utils/return_anno.py b/pydoclint/utils/return_anno.py
index 603c8e9..702f059 100644
--- a/pydoclint/utils/return_anno.py
+++ b/pydoclint/utils/return_anno.py
@@ -1,6 +1,7 @@
+from __future__ import annotations
+
 import ast
 import json
-from typing import List, Optional
 
 from pydoclint.utils.edge_case_error import EdgeCaseError
 from pydoclint.utils.generic import stripQuotes
@@ -10,8 +11,8 @@
 class ReturnAnnotation:
     """A class to hold the return annotation in a function's signature"""
 
-    def __init__(self, annotation: Optional[str]) -> None:
-        self.annotation: Optional[str] = stripQuotes(annotation)
+    def __init__(self, annotation: str | None) -> None:
+        self.annotation: str | None = stripQuotes(annotation)
 
     def __str__(self) -> str:
         return f'ReturnAnnotation(annotation={json.dumps(self.annotation)})'
@@ -19,7 +20,7 @@ def __str__(self) -> str:
     def __repr__(self) -> str:
         return self.__str__()
 
-    def decompose(self) -> List[str]:
+    def decompose(self) -> list[str]:
         """
         Numpy style allows decomposing the returning tuple into individual
         element.  For example, if the return annotation is `Tuple[int, bool]`,
@@ -29,7 +30,7 @@ def decompose(self) -> List[str]:
 
         Returns
         -------
-        List[str]
+        list[str]
             The decomposed element
 
         Raises
@@ -59,7 +60,7 @@ def decompose(self) -> List[str]:
                 return [insideTuple]
 
             if isinstance(parsedBody0.value, ast.Tuple):  # like Tuple[int, str]
-                elts: List[ast.expr] = parsedBody0.value.elts
+                elts: list[ast.expr] = parsedBody0.value.elts
                 return [unparseName(_) for _ in elts]  # type:ignore[misc]
 
             raise EdgeCaseError('decompose(): This should not have happened')
@@ -74,6 +75,6 @@ def _isTuple(self) -> bool:
         except Exception:
             return False
 
-    def putAnnotationInList(self) -> List[str]:
+    def putAnnotationInList(self) -> list[str]:
         """Put annotation string in a list"""
         return [] if self.annotation is None else [self.annotation]
diff --git a/pydoclint/utils/return_yield_raise.py b/pydoclint/utils/return_yield_raise.py
index a94a6d7..a62d062 100644
--- a/pydoclint/utils/return_yield_raise.py
+++ b/pydoclint/utils/return_yield_raise.py
@@ -1,5 +1,7 @@
+from __future__ import annotations
+
 import ast
-from typing import Callable, Dict, Generator, List, Optional, Tuple, Type
+from typing import Callable, Generator, Type
 
 from pydoclint.utils import walk
 from pydoclint.utils.astTypes import BlockType, FuncOrAsyncFuncDef
@@ -8,8 +10,8 @@
 
 ReturnType = Type[ast.Return]
 ExprType = Type[ast.expr]
-YieldAndYieldFromTypes = Tuple[Type[ast.Yield], Type[ast.YieldFrom]]
-FuncOrAsyncFuncTypes = Tuple[Type[ast.FunctionDef], Type[ast.AsyncFunctionDef]]
+YieldAndYieldFromTypes = tuple[Type[ast.Yield], Type[ast.YieldFrom]]
+FuncOrAsyncFuncTypes = tuple[Type[ast.FunctionDef], Type[ast.AsyncFunctionDef]]
 FuncOrAsyncFunc = (ast.FunctionDef, ast.AsyncFunctionDef)
 
 
@@ -23,7 +25,7 @@ def isReturnAnnotationNone(node: FuncOrAsyncFuncDef) -> bool:
     return _isNone(node.returns)
 
 
-def _isNone(node: Optional[ast.expr]) -> bool:
+def _isNone(node: ast.expr | None) -> bool:
     return isinstance(node, ast.Constant) and node.value is None
 
 
@@ -32,7 +34,7 @@ def isReturnAnnotationNoReturn(node: FuncOrAsyncFuncDef) -> bool:
     if node.returns is None:
         return False
 
-    returnAnnotation: Optional[str] = unparseName(node.returns)
+    returnAnnotation: str | None = unparseName(node.returns)
     return returnAnnotation == 'NoReturn'
 
 
@@ -41,7 +43,7 @@ def hasGeneratorAsReturnAnnotation(node: FuncOrAsyncFuncDef) -> bool:
     if node.returns is None:
         return False
 
-    returnAnno: Optional[str] = unparseName(node.returns)
+    returnAnno: str | None = unparseName(node.returns)
     return returnAnno in {'Generator', 'AsyncGenerator'} or stringStartsWith(
         returnAnno, ('Generator[', 'AsyncGenerator[')
     )
@@ -52,7 +54,7 @@ def hasIteratorOrIterableAsReturnAnnotation(node: FuncOrAsyncFuncDef) -> bool:
     if node.returns is None:
         return False
 
-    returnAnnotation: Optional[str] = unparseName(node.returns)
+    returnAnnotation: str | None = unparseName(node.returns)
     return returnAnnotation in {
         'Iterator',
         'Iterable',
@@ -93,7 +95,7 @@ def isThisNodeARaiseStmt(node_: ast.AST) -> bool:
     return _hasExpectedStatements(node, isThisNodeARaiseStmt)
 
 
-def getRaisedExceptions(node: FuncOrAsyncFuncDef) -> List[str]:
+def getRaisedExceptions(node: FuncOrAsyncFuncDef) -> list[str]:
     """Get the raised exceptions in a function node as a sorted list"""
     return sorted(set(_getRaisedExceptions(node)))
 
@@ -105,9 +107,9 @@ def _getRaisedExceptions(
     childLineNum: int = -999
 
     # key: child lineno, value: (parent lineno, is parent a function?)
-    familyTree: Dict[int, Tuple[int, bool]] = {}
+    familyTree: dict[int, tuple[int, bool]] = {}
 
-    currentParentExceptHandler: Optional[ast.ExceptHandler] = None
+    currentParentExceptHandler: ast.ExceptHandler | None = None
 
     # Depth-first guarantees the last-seen exception handler
     # is a parent of child.
@@ -198,7 +200,7 @@ def _hasExpectedStatements(
     foundExpectedStmt: bool = False
 
     # key: child lineno, value: (parent lineno, is parent a function?)
-    familyTree: Dict[int, Tuple[int, bool]] = {}
+    familyTree: dict[int, tuple[int, bool]] = {}
 
     for child, parent in walk.walk(node):
         childLineNum = _updateFamilyTree(child, parent, familyTree)
@@ -223,7 +225,7 @@ def _hasExpectedStatements(
 def _updateFamilyTree(
         child: ast.AST,
         parent: ast.AST,
-        familyTree: Dict[int, Tuple[int, bool]],
+        familyTree: dict[int, tuple[int, bool]],
 ) -> int:
     """
     Structure of `familyTree`:
@@ -256,7 +258,7 @@ def _getLineNum(node: ast.AST) -> int:
 
 def _confirmThisStmtIsNotWithinNestedFunc(
         foundStatementTemp: bool,
-        familyTree: Dict[int, Tuple[int, bool]],
+        familyTree: dict[int, tuple[int, bool]],
         lineNumOfStatement: int,
         lineNumOfThisNode: int,
 ) -> bool:
@@ -278,7 +280,7 @@ def _confirmThisStmtIsNotWithinNestedFunc(
 
 
 def _lookupParentFunc(
-        familyLine: Dict[int, Tuple[int, bool]],
+        familyLine: dict[int, tuple[int, bool]],
         lineNumOfChildNode: int,
 ) -> int:
     """
diff --git a/pydoclint/utils/unparser_custom.py b/pydoclint/utils/unparser_custom.py
index df6cf33..d3c3a9e 100644
--- a/pydoclint/utils/unparser_custom.py
+++ b/pydoclint/utils/unparser_custom.py
@@ -1,7 +1,8 @@
+from __future__ import annotations
+
 import ast
 import re
 import sys
-from typing import Optional, Union
 
 from pydoclint.utils.edge_case_error import EdgeCaseError
 
@@ -31,8 +32,8 @@ def py311unparse(astObj: ast.AST) -> str:
 
 
 def unparseName(
-        node: Union[ast.expr, ast.Module, None],
-) -> Optional[str]:
+        node: ast.expr | ast.Module | None,
+) -> str | None:
     """Parse type annotations from argument list or return annotation."""
     if node is None:
         return None
diff --git a/pydoclint/utils/violation.py b/pydoclint/utils/violation.py
index 92207c9..965d84e 100644
--- a/pydoclint/utils/violation.py
+++ b/pydoclint/utils/violation.py
@@ -1,6 +1,7 @@
+from __future__ import annotations
+
 import types
 from copy import deepcopy
-from typing import Tuple
 
 from pydoclint.utils.edge_case_error import EdgeCaseError
 
@@ -108,7 +109,7 @@ def _str(self, showLineNum: bool = False) -> str:
 
         return f'{self.line}: {self.__str__()}'
 
-    def getInfoForFlake8(self) -> Tuple[int, int, str]:
+    def getInfoForFlake8(self) -> tuple[int, int, str]:
         """Get the violation info for flake8"""
         colOffset: int = 0  # we don't need column offset to locate the issue
         msg = f'{self.fullErrorCode} {self.msg}'  # no colon b/c that would cause 'yesqa' issues
diff --git a/pydoclint/utils/visitor_helper.py b/pydoclint/utils/visitor_helper.py
index 743bc7b..c08b8a0 100644
--- a/pydoclint/utils/visitor_helper.py
+++ b/pydoclint/utils/visitor_helper.py
@@ -1,7 +1,8 @@
 """Helper functions to classes/methods in visitor.py"""
+from __future__ import annotations
+
 import ast
 import sys
-from typing import List, Optional, Set
 
 from pydoclint.utils.arg import Arg, ArgList
 from pydoclint.utils.doc import Doc
@@ -30,7 +31,7 @@ def checkClassAttributesAgainstClassDocstring(
         *,
         node: ast.ClassDef,
         style: str,
-        violations: List[Violation],
+        violations: list[Violation],
         lineNum: int,
         msgPrefix: str,
         shouldCheckArgOrder: bool,
@@ -153,7 +154,7 @@ def extractClassAttributesFromNode(
     if 'body' not in node.__dict__ or len(node.body) == 0:
         return ArgList([])
 
-    atl: List[Arg] = []
+    atl: list[Arg] = []
     for itm in node.body:
         if isinstance(itm, ast.AnnAssign):  # with type hints ("a: int = 1")
             atl.append(Arg.fromAstAnnAssign(itm))
@@ -184,7 +185,7 @@ def checkDocArgsLengthAgainstActualArgs(
         *,
         docArgs: ArgList,
         actualArgs: ArgList,
-        violations: List[Violation],
+        violations: list[Violation],
         violationForDocArgsLengthShorter: Violation,  # such as V101, V601
         violationForDocArgsLengthLonger: Violation,  # such as V102, V602
 ) -> None:
@@ -200,7 +201,7 @@ def checkNameOrderAndTypeHintsOfDocArgsAgainstActualArgs(
         *,
         docArgs: ArgList,
         actualArgs: ArgList,
-        violations: List[Violation],
+        violations: list[Violation],
         actualArgsAreClassAttributes: bool,
         violationForOrderMismatch: Violation,  # such as V104, V604
         violationForTypeHintMismatch: Violation,  # such as V105, V605
@@ -250,16 +251,16 @@ def checkNameOrderAndTypeHintsOfDocArgsAgainstActualArgs(
             violations.append(violationForOrderMismatch)
             violations.append(v105new)
         else:
-            argsInFuncNotInDoc: Set[Arg] = actualArgs.subtract(
+            argsInFuncNotInDoc: set[Arg] = actualArgs.subtract(
                 docArgs,
                 checkTypeHint=False,
             )
-            argsInDocNotInFunc: Set[Arg] = docArgs.subtract(
+            argsInDocNotInFunc: set[Arg] = docArgs.subtract(
                 actualArgs,
                 checkTypeHint=False,
             )
 
-            msgPostfixParts: List[str] = []
+            msgPostfixParts: list[str] = []
 
             string0 = (
                 'Attributes in the class definition but not in the'
@@ -304,8 +305,8 @@ def checkReturnTypesForViolations(
         *,
         style: str,
         returnAnnotation: ReturnAnnotation,
-        violationList: List[Violation],
-        returnSection: List[ReturnArg],
+        violationList: list[Violation],
+        returnSection: list[ReturnArg],
         violation: Violation,
 ) -> None:
     """Check return types between function signature and docstring"""
@@ -328,8 +329,8 @@ def checkReturnTypesForViolations(
 def checkReturnTypesForNumpyStyle(
         *,
         returnAnnotation: ReturnAnnotation,
-        violationList: List[Violation],
-        returnSection: List[ReturnArg],
+        violationList: list[Violation],
+        returnSection: list[ReturnArg],
         violation: Violation,
 ) -> None:
     """Check return types for numpy docstring style"""
@@ -352,10 +353,10 @@ def checkReturnTypesForNumpyStyle(
     #
     #  This is why we are comparing both the decomposed annotation
     #  types and the original annotation type
-    returnAnnoItems: List[str] = returnAnnotation.decompose()
-    returnAnnoInList: List[str] = returnAnnotation.putAnnotationInList()
+    returnAnnoItems: list[str] = returnAnnotation.decompose()
+    returnAnnoInList: list[str] = returnAnnotation.putAnnotationInList()
 
-    returnSecTypes: List[str] = [stripQuotes(_.argType) for _ in returnSection]  # type:ignore[misc]
+    returnSecTypes: list[str] = [stripQuotes(_.argType) for _ in returnSection]  # type:ignore[misc]
 
     if returnAnnoInList != returnSecTypes:
         if len(returnAnnoItems) != len(returnSection):
@@ -376,8 +377,8 @@ def checkReturnTypesForNumpyStyle(
 def checkReturnTypesForGoogleOrSphinxStyle(
         *,
         returnAnnotation: ReturnAnnotation,
-        violationList: List[Violation],
-        returnSection: List[ReturnArg],
+        violationList: list[Violation],
+        returnSection: list[ReturnArg],
         violation: Violation,
 ) -> None:
     """Check return types for Google or Sphinx docstring style"""
@@ -410,8 +411,8 @@ def checkReturnTypesForGoogleOrSphinxStyle(
 def checkYieldTypesForViolations(
         *,
         returnAnnotation: ReturnAnnotation,
-        violationList: List[Violation],
-        yieldSection: List[YieldArg],
+        violationList: list[Violation],
+        yieldSection: list[YieldArg],
         violation: Violation,
         hasGeneratorAsReturnAnnotation: bool,
         hasIteratorOrIterableAsReturnAnnotation: bool,
@@ -425,10 +426,10 @@ def checkYieldTypesForViolations(
     # values into one `Generator[..., ..., ...]`, because it is easier
     # to check and less ambiguous.
 
-    returnAnnoText: Optional[str] = returnAnnotation.annotation
+    returnAnnoText: str | None = returnAnnotation.annotation
 
     extract = extractYieldTypeFromGeneratorOrIteratorAnnotation
-    yieldType: Optional[str] = extract(
+    yieldType: str | None = extract(
         returnAnnoText,
         hasGeneratorAsReturnAnnotation,
         hasIteratorOrIterableAsReturnAnnotation,
@@ -469,10 +470,10 @@ def checkYieldTypesForViolations(
 
 
 def extractYieldTypeFromGeneratorOrIteratorAnnotation(
-        returnAnnoText: Optional[str],
+        returnAnnoText: str | None,
         hasGeneratorAsReturnAnnotation: bool,
         hasIteratorOrIterableAsReturnAnnotation: bool,
-) -> Optional[str]:
+) -> str | None:
     """Extract yield type from Generator or Iterator annotations"""
     #
     # "Yield type" is the 0th element in a Generator
@@ -480,7 +481,7 @@ def extractYieldTypeFromGeneratorOrIteratorAnnotation(
     # ReturnType])
     # https://docs.python.org/3/library/typing.html#typing.Generator
     # Or it's the 0th (only) element in Iterator
-    yieldType: Optional[str]
+    yieldType: str | None
 
     try:
         if hasGeneratorAsReturnAnnotation:
@@ -504,16 +505,14 @@ def extractYieldTypeFromGeneratorOrIteratorAnnotation(
     return stripQuotes(yieldType)
 
 
-def extractReturnTypeFromGenerator(
-        returnAnnoText: Optional[str],
-) -> Optional[str]:
+def extractReturnTypeFromGenerator(returnAnnoText: str | None) -> str | None:
     """Extract return type from Generator annotations"""
     #
     # "Return type" is the last element in a Generator
     # type annotation (Generator[YieldType, SendType,
     # ReturnType])
     # https://docs.python.org/3/library/typing.html#typing.Generator
-    returnType: Optional[str]
+    returnType: str | None
     try:
         if sys.version_info >= (3, 9):
             returnType = unparseName(
@@ -531,9 +530,9 @@ def extractReturnTypeFromGenerator(
 
 def addMismatchedRaisesExceptionViolation(
         *,
-        docRaises: List[str],
-        actualRaises: List[str],
-        violations: List[Violation],
+        docRaises: list[str],
+        actualRaises: list[str],
+        violations: list[Violation],
         violationForRaisesMismatch: Violation,  # such as V503
         lineNum: int,
         msgPrefix: str,
diff --git a/pydoclint/visitor.py b/pydoclint/visitor.py
index eb94c7e..33c8692 100644
--- a/pydoclint/visitor.py
+++ b/pydoclint/visitor.py
@@ -1,5 +1,6 @@
+from __future__ import annotations
+
 import ast
-from typing import List, Optional, Union
 
 from pydoclint.utils.arg import Arg, ArgList
 from pydoclint.utils.astTypes import FuncOrAsyncFuncDef
@@ -91,7 +92,7 @@ def __init__(
         )
 
         self.parent: ast.AST = ast.Pass()  # keep track of parent node
-        self.violations: List[Violation] = []
+        self.violations: list[Violation] = []
 
     def visit_ClassDef(self, node: ast.ClassDef) -> None:  # noqa: D102
         currentParent = self.parent  # keep aside
@@ -121,7 +122,7 @@ def visit_ClassDef(self, node: ast.ClassDef) -> None:  # noqa: D102
         self.parent = currentParent  # restore
 
     def visit_FunctionDef(self, node: FuncOrAsyncFuncDef) -> None:  # noqa: D102
-        parent_: Union[ast.ClassDef, FuncOrAsyncFuncDef] = self.parent  # type:ignore[assignment]
+        parent_: ast.ClassDef | FuncOrAsyncFuncDef = self.parent  # type:ignore[assignment]
         self.parent = node
 
         isClassConstructor: bool = node.name == '__init__' and isinstance(
@@ -140,10 +141,10 @@ def visit_FunctionDef(self, node: FuncOrAsyncFuncDef) -> None:  # noqa: D102
                 initDocstring=docstring,
             )
 
-        argViolations: List[Violation]
-        returnViolations: List[Violation]
-        yieldViolations: List[Violation]
-        raiseViolations: List[Violation]
+        argViolations: list[Violation]
+        returnViolations: list[Violation]
+        yieldViolations: list[Violation]
+        raiseViolations: list[Violation]
 
         if docstring == '':
             # We don't check functions without docstrings.
@@ -357,7 +358,7 @@ def checkArguments(  # noqa: C901
             node: FuncOrAsyncFuncDef,
             parent_: ast.AST,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """
         Check input arguments of the function.
 
@@ -374,10 +375,10 @@ def checkArguments(  # noqa: C901
 
         Returns
         -------
-        List[Violation]
+        list[Violation]
             A list of argument violations
         """
-        astArgList: List[ast.arg] = collectFuncArgs(node)
+        astArgList: list[ast.arg] = collectFuncArgs(node)
 
         isMethod: bool = isinstance(parent_, ast.ClassDef)
         msgPrefix: str = generateFuncMsgPrefix(node, parent_, appendColon=True)
@@ -414,7 +415,7 @@ def checkArguments(  # noqa: C901
         if docArgs.length == 0 and funcArgs.length == 0:
             return []
 
-        violations: List[Violation] = []
+        violations: list[Violation] = []
 
         checkDocArgsLengthAgainstActualArgs(
             docArgs=docArgs,
@@ -473,7 +474,7 @@ def checkReturns(  # noqa: C901
             node: FuncOrAsyncFuncDef,
             parent: ast.AST,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """Check return statement & return type annotation of this function"""
         lineNum: int = node.lineno
         msgPrefix = generateFuncMsgPrefix(node, parent, appendColon=False)
@@ -492,7 +493,7 @@ def checkReturns(  # noqa: C901
 
         docstringHasReturnSection: bool = doc.hasReturnsSection
 
-        violations: List[Violation] = []
+        violations: list[Violation] = []
         if not docstringHasReturnSection and not isPropertyMethod:
             if (
                 # fmt: off
@@ -525,7 +526,7 @@ def checkReturns(  # noqa: C901
                 returnAnno = ReturnAnnotation(annotation=None)
 
             if docstringHasReturnSection:
-                returnSec: List[ReturnArg] = doc.returnSection
+                returnSec: list[ReturnArg] = doc.returnSection
             else:
                 returnSec = []
 
@@ -566,9 +567,9 @@ def checkReturnsAndYieldsInClassConstructor(
             cls,
             parent: ast.ClassDef,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """Check the presence of a Returns/Yields section in class docstring"""
-        violations: List[Violation] = []
+        violations: list[Violation] = []
         if doc.hasReturnsSection:
             violations.append(
                 Violation(
@@ -594,9 +595,9 @@ def checkYields(  # noqa: C901
             node: FuncOrAsyncFuncDef,
             parent: ast.AST,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """Check violations on 'yield' statements or 'Generator' annotation"""
-        violations: List[Violation] = []
+        violations: list[Violation] = []
 
         lineNum: int = node.lineno
         msgPrefix = generateFuncMsgPrefix(node, parent, appendColon=False)
@@ -621,7 +622,7 @@ def checkYields(  # noqa: C901
 
         if not docstringHasYieldsSection:
             extract = extractYieldTypeFromGeneratorOrIteratorAnnotation
-            yieldType: Optional[str] = extract(
+            yieldType: str | None = extract(
                 returnAnnoText=returnAnno.annotation,
                 hasGeneratorAsReturnAnnotation=hasGenAsRetAnno,
                 hasIteratorOrIterableAsReturnAnnotation=hasIterAsRetAnno,
@@ -645,7 +646,7 @@ def checkYields(  # noqa: C901
 
         if hasYieldStmt and self.checkYieldTypes:
             if docstringHasYieldsSection:
-                yieldSec: List[YieldArg] = doc.yieldSection
+                yieldSec: list[YieldArg] = doc.yieldSection
             else:
                 yieldSec = []
 
@@ -668,7 +669,7 @@ def checkReturnAndYield(  # noqa: C901
             node: FuncOrAsyncFuncDef,
             parent: ast.AST,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """
         Check violations when a function has both `return` and `yield`
         statements in it.
@@ -699,7 +700,7 @@ def my_function(num: int) -> Generator[int, None, str]:
         # Just a sanity check:
         assert (hasYieldStatements(node) and hasReturnStatements(node)) is True
 
-        violations: List[Violation] = []
+        violations: list[Violation] = []
 
         lineNum: int = node.lineno
         msgPrefix = generateFuncMsgPrefix(node, parent, appendColon=False)
@@ -722,10 +723,10 @@ def my_function(num: int) -> Generator[int, None, str]:
         hasReturnAnno: bool = hasReturnAnnotation(node)
 
         returnAnno = ReturnAnnotation(unparseName(node.returns))
-        returnSec: List[ReturnArg] = doc.returnSection
+        returnSec: list[ReturnArg] = doc.returnSection
 
         # Check the return section in the docstring
-        retTypeInGenerator: Optional[str]
+        retTypeInGenerator: str | None
         if not docstringHasReturnSection:
             if doc.isShortDocstring and self.skipCheckingShortDocstrings:
                 pass
@@ -775,11 +776,11 @@ def my_function(num: int) -> Generator[int, None, str]:
         else:
             if self.checkYieldTypes:
                 returnAnno = ReturnAnnotation(unparseName(node.returns))
-                yieldSec: List[YieldArg] = doc.yieldSection
+                yieldSec: list[YieldArg] = doc.yieldSection
 
                 if hasGenAsRetAnno or hasIterAsRetAnno:
                     extract = extractYieldTypeFromGeneratorOrIteratorAnnotation
-                    yieldType: Optional[str] = extract(
+                    yieldType: str | None = extract(
                         returnAnnoText=returnAnno.annotation,
                         hasGeneratorAsReturnAnnotation=hasGenAsRetAnno,
                         hasIteratorOrIterableAsReturnAnnotation=hasIterAsRetAnno,
@@ -808,9 +809,9 @@ def checkRaises(
             node: FuncOrAsyncFuncDef,
             parent: ast.AST,
             doc: Doc,
-    ) -> List[Violation]:
+    ) -> list[Violation]:
         """Check violations on 'raise' statements"""
-        violations: List[Violation] = []
+        violations: list[Violation] = []
 
         lineNum: int = node.lineno
         msgPrefix = generateFuncMsgPrefix(node, parent, appendColon=False)
@@ -831,7 +832,7 @@ def checkRaises(
 
         # check that the raise statements match those in body.
         if hasRaiseStmt:
-            docRaises: List[str] = []
+            docRaises: list[str] = []
 
             for raises in doc.parsed.raises:
                 if raises.type_name: