diff --git a/doc/api/next_api_changes/deprecations/30163-AL.rst b/doc/api/next_api_changes/deprecations/30163-AL.rst
@@ -0,0 +1,9 @@
+``matplotlib.style.core``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+The ``matplotlib.style.core`` module is deprecated.  All APIs intended for
+public use are now available in `matplotlib.style` directly (including
+``USER_LIBRARY_PATHS``, which was previously not reexported).
+
+The following APIs of ``matplotlib.style.core`` have been deprecated with no
+replacement: ``BASE_LIBRARY_PATH``, ``STYLE_EXTENSION``, ``STYLE_BLACKLIST``,
+``update_user_library``, ``read_style_directory``, ``update_nested_dict``.
diff --git a/lib/matplotlib/style/__init__.py b/lib/matplotlib/style/__init__.py
@@ -1,4 +1,252 @@
-from .core import available, context, library, reload_library, use
+"""
+Core functions and attributes for the matplotlib style library:
 
+``use``
+    Select style sheet to override the current matplotlib settings.
+``context``
+    Context manager to use a style sheet temporarily.
+``available``
+    List available style sheets.
+``library``
+    A dictionary of style names and matplotlib settings.
+"""
 
-__all__ = ["available", "context", "library", "reload_library", "use"]
+import contextlib
+import importlib.resources
+import logging
+import os
+from pathlib import Path
+import warnings
+
+import matplotlib as mpl
+from matplotlib import _api, _docstring, rc_params_from_file, rcParamsDefault
+
+_log = logging.getLogger(__name__)
+
+__all__ = ['use', 'context', 'available', 'library', 'reload_library']
+
+
+_BASE_LIBRARY_PATH = os.path.join(mpl.get_data_path(), 'stylelib')
+# Users may want multiple library paths, so store a list of paths.
+USER_LIBRARY_PATHS = [os.path.join(mpl.get_configdir(), 'stylelib')]
+_STYLE_EXTENSION = 'mplstyle'
+# A list of rcParams that should not be applied from styles
+_STYLE_BLACKLIST = {
+    'interactive', 'backend', 'webagg.port', 'webagg.address',
+    'webagg.port_retries', 'webagg.open_in_browser', 'backend_fallback',
+    'toolbar', 'timezone', 'figure.max_open_warning',
+    'figure.raise_window', 'savefig.directory', 'tk.window_focus',
+    'docstring.hardcopy', 'date.epoch'}
+
+
+@_docstring.Substitution(
+    "\n".join(map("- {}".format, sorted(_STYLE_BLACKLIST, key=str.lower)))
+)
+def use(style):
+    """
+    Use Matplotlib style settings from a style specification.
+
+    The style name of 'default' is reserved for reverting back to
+    the default style settings.
+
+    .. note::
+
+       This updates the `.rcParams` with the settings from the style.
+       `.rcParams` not defined in the style are kept.
+
+    Parameters
+    ----------
+    style : str, dict, Path or list
+
+        A style specification. Valid options are:
+
+        str
+            - One of the style names in `.style.available` (a builtin style or
+              a style installed in the user library path).
+
+            - A dotted name of the form "package.style_name"; in that case,
+              "package" should be an importable Python package name, e.g. at
+              ``/path/to/package/__init__.py``; the loaded style file is
+              ``/path/to/package/style_name.mplstyle``.  (Style files in
+              subpackages are likewise supported.)
+
+            - The path or URL to a style file, which gets loaded by
+              `.rc_params_from_file`.
+
+        dict
+            A mapping of key/value pairs for `matplotlib.rcParams`.
+
+        Path
+            The path to a style file, which gets loaded by
+            `.rc_params_from_file`.
+
+        list
+            A list of style specifiers (str, Path or dict), which are applied
+            from first to last in the list.
+
+    Notes
+    -----
+    The following `.rcParams` are not related to style and will be ignored if
+    found in a style specification:
+
+    %s
+    """
+    if isinstance(style, (str, Path)) or hasattr(style, 'keys'):
+        # If name is a single str, Path or dict, make it a single element list.
+        styles = [style]
+    else:
+        styles = style
+
+    style_alias = {'mpl20': 'default', 'mpl15': 'classic'}
+
+    for style in styles:
+        if isinstance(style, str):
+            style = style_alias.get(style, style)
+            if style == "default":
+                # Deprecation warnings were already handled when creating
+                # rcParamsDefault, no need to reemit them here.
+                with _api.suppress_matplotlib_deprecation_warning():
+                    # don't trigger RcParams.__getitem__('backend')
+                    style = {k: rcParamsDefault[k] for k in rcParamsDefault
+                             if k not in _STYLE_BLACKLIST}
+            elif style in library:
+                style = library[style]
+            elif "." in style:
+                pkg, _, name = style.rpartition(".")
+                try:
+                    path = importlib.resources.files(pkg) / f"{name}.{_STYLE_EXTENSION}"
+                    style = rc_params_from_file(path, use_default_template=False)
+                except (ModuleNotFoundError, OSError, TypeError) as exc:
+                    # There is an ambiguity whether a dotted name refers to a
+                    # package.style_name or to a dotted file path.  Currently,
+                    # we silently try the first form and then the second one;
+                    # in the future, we may consider forcing file paths to
+                    # either use Path objects or be prepended with "./" and use
+                    # the slash as marker for file paths.
+                    pass
+        if isinstance(style, (str, Path)):
+            try:
+                style = rc_params_from_file(style, use_default_template=False)
+            except OSError as err:
+                raise OSError(
+                    f"{style!r} is not a valid package style, path of style "
+                    f"file, URL of style file, or library style name (library "
+                    f"styles are listed in `style.available`)") from err
+        filtered = {}
+        for k in style:  # don't trigger RcParams.__getitem__('backend')
+            if k in _STYLE_BLACKLIST:
+                _api.warn_external(
+                    f"Style includes a parameter, {k!r}, that is not "
+                    f"related to style.  Ignoring this parameter.")
+            else:
+                filtered[k] = style[k]
+        mpl.rcParams.update(filtered)
+
+
+@contextlib.contextmanager
+def context(style, after_reset=False):
+    """
+    Context manager for using style settings temporarily.
+
+    Parameters
+    ----------
+    style : str, dict, Path or list
+        A style specification. Valid options are:
+
+        str
+            - One of the style names in `.style.available` (a builtin style or
+              a style installed in the user library path).
+
+            - A dotted name of the form "package.style_name"; in that case,
+              "package" should be an importable Python package name, e.g. at
+              ``/path/to/package/__init__.py``; the loaded style file is
+              ``/path/to/package/style_name.mplstyle``.  (Style files in
+              subpackages are likewise supported.)
+
+            - The path or URL to a style file, which gets loaded by
+              `.rc_params_from_file`.
+        dict
+            A mapping of key/value pairs for `matplotlib.rcParams`.
+
+        Path
+            The path to a style file, which gets loaded by
+            `.rc_params_from_file`.
+
+        list
+            A list of style specifiers (str, Path or dict), which are applied
+            from first to last in the list.
+
+    after_reset : bool
+        If True, apply style after resetting settings to their defaults;
+        otherwise, apply style on top of the current settings.
+    """
+    with mpl.rc_context():
+        if after_reset:
+            mpl.rcdefaults()
+        use(style)
+        yield
+
+
+def _update_user_library(library):
+    """Update style library with user-defined rc files."""
+    for stylelib_path in map(os.path.expanduser, USER_LIBRARY_PATHS):
+        styles = _read_style_directory(stylelib_path)
+        _update_nested_dict(library, styles)
+    return library
+
+
+@_api.deprecated("3.11")
+def update_user_library(library):
+    return _update_user_library(library)
+
+
+def _read_style_directory(style_dir):
+    """Return dictionary of styles defined in *style_dir*."""
+    styles = dict()
+    for path in Path(style_dir).glob(f"*.{_STYLE_EXTENSION}"):
+        with warnings.catch_warnings(record=True) as warns:
+            styles[path.stem] = rc_params_from_file(path, use_default_template=False)
+        for w in warns:
+            _log.warning('In %s: %s', path, w.message)
+    return styles
+
+
+@_api.deprecated("3.11")
+def read_style_directory(style_dir):
+    return _read_style_directory(style_dir)
+
+
+def _update_nested_dict(main_dict, new_dict):
+    """
+    Update nested dict (only level of nesting) with new values.
+
+    Unlike `dict.update`, this assumes that the values of the parent dict are
+    dicts (or dict-like), so you shouldn't replace the nested dict if it
+    already exists. Instead you should update the sub-dict.
+    """
+    # update named styles specified by user
+    for name, rc_dict in new_dict.items():
+        main_dict.setdefault(name, {}).update(rc_dict)
+    return main_dict
+
+
+@_api.deprecated("3.11")
+def update_nested_dict(main_dict, new_dict):
+    return _update_nested_dict(main_dict, new_dict)
+
+
+# Load style library
+# ==================
+_base_library = _read_style_directory(_BASE_LIBRARY_PATH)
+library = {}
+available = []
+
+
+def reload_library():
+    """Reload the style library."""
+    library.clear()
+    library.update(_update_user_library(_base_library))
+    available[:] = sorted(library.keys())
+
+
+reload_library()
diff --git a/lib/matplotlib/style/__init__.pyi b/lib/matplotlib/style/__init__.pyi
@@ -0,0 +1,20 @@
+from collections.abc import Generator
+import contextlib
+
+from matplotlib import RcParams
+from matplotlib.typing import RcStyleType
+
+USER_LIBRARY_PATHS: list[str] = ...
+
+def use(style: RcStyleType) -> None: ...
+@contextlib.contextmanager
+def context(
+    style: RcStyleType, after_reset: bool = ...
+) -> Generator[None, None, None]: ...
+
+library: dict[str, RcParams]
+available: list[str]
+
+def reload_library() -> None: ...
+
+__all__ = ['use', 'context', 'available', 'library', 'reload_library']