diff --git a/CHANGES.rst b/CHANGES.rst
index a332e406..23bc99ec 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -6,6 +6,9 @@ Version 2.0.0
 Unreleased
 
 -   Drop support for Python 2 and 3.5.
+-   JSON support no longer uses simplejson. To use another JSON module,
+    override ``app.json_encoder`` and ``json_decoder``. :issue:`3555`
+-   The ``encoding`` option to JSON functions is deprecated. :pr:`3562`
 -   Add :meth:`sessions.SessionInterface.get_cookie_name` to allow
     setting the session cookie name dynamically. :pr:`3369`
 -   Add :meth:`Config.from_file` to load config using arbitrary file
@@ -19,9 +22,6 @@ Unreleased
     200 OK and an empty file. :issue:`3358`
 -   When using ad-hoc certificates, check for the cryptography library
     instead of PyOpenSSL. :pr:`3492`
--   JSON support no longer uses simplejson if it's installed. To use
-    another JSON module, override ``app.json_encoder`` and
-    ``json_decoder``. :issue:`3555`
 
 
 Version 1.1.2
diff --git a/docs/api.rst b/docs/api.rst
index 97c1c7a1..351d9b87 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -279,45 +279,34 @@ Message Flashing
 
 .. autofunction:: get_flashed_messages
 
+
 JSON Support
 ------------
 
 .. module:: flask.json
 
-Flask uses the built-in :mod:`json` module for the JSON implementation.
-It will delegate access to the current application's JSON encoders and
-decoders for easier customization.
+Flask uses the built-in :mod:`json` module for handling JSON. It will
+use the current blueprint's or application's JSON encoder and decoder
+for easier customization. By default it handles some extra data types:
 
-For usage examples, read the :mod:`json` documentation in the standard
-library.  The following extensions are by default applied to the stdlib's
-JSON module:
+-   :class:`datetime.datetime` and :class:`datetime.date` are serialized
+    to :rfc:`822` strings. This is the same as the HTTP date format.
+-   :class:`uuid.UUID` is serialized to a string.
+-   :class:`dataclasses.dataclass` is passed to
+    :func:`dataclasses.asdict`.
+-   :class:`~markupsafe.Markup` (or any object with a ``__html__``
+    method) will call the ``__html__`` method to get a string.
 
-1.  ``datetime`` objects are serialized as :rfc:`822` strings.
-2.  Any object with an ``__html__`` method (like :class:`~flask.Markup`)
-    will have that method called and then the return value is serialized
-    as string.
-
-The :func:`~htmlsafe_dumps` function of this json module is also available
-as a filter called ``|tojson`` in Jinja2.  Note that in versions of Flask prior
-to Flask 0.10, you must disable escaping with ``|safe`` if you intend to use
-``|tojson`` output inside ``script`` tags. In Flask 0.10 and above, this
-happens automatically (but it's harmless to include ``|safe`` anyway).
+:func:`~htmlsafe_dumps` is also available as the ``|tojson`` template
+filter. The filter marks the output with ``|safe`` so it can be used
+inside ``script`` tags.
 
 .. sourcecode:: html+jinja
 
     <script type=text/javascript>
-        doSomethingWith({{ user.username|tojson|safe }});
+        renderChart({{ axis_data|tojson }});
     </script>
 
-.. admonition:: Auto-Sort JSON Keys
-
-    The configuration variable :data:`JSON_SORT_KEYS` can be set to
-    ``False`` to stop Flask from auto-sorting keys. By default sorting
-    is enabled and outside of the app context sorting is turned on.
-
-    Notice that disabling key sorting can cause issues when using
-    content  based HTTP caches and Python's hash randomization feature.
-
 .. autofunction:: jsonify
 
 .. autofunction:: dumps
@@ -336,6 +325,7 @@ happens automatically (but it's harmless to include ``|safe`` anyway).
 
 .. automodule:: flask.json.tag
 
+
 Template Rendering
 ------------------
 
diff --git a/src/flask/json/__init__.py b/src/flask/json/__init__.py
index 3e9c21a6..6ef22e26 100644
--- a/src/flask/json/__init__.py
+++ b/src/flask/json/__init__.py
@@ -19,33 +19,27 @@ except ImportError:
 
 
 class JSONEncoder(_json.JSONEncoder):
-    """The default Flask JSON encoder. This one extends the default
-    encoder by also supporting ``datetime``, ``UUID``, ``dataclasses``,
-    and ``Markup`` objects.
+    """The default JSON encoder. Handles extra types compared to the
+    built-in :class:`json.JSONEncoder`.
 
-    ``datetime`` objects are serialized as RFC 822 datetime strings.
-    This is the same as the HTTP date format.
+    -   :class:`datetime.datetime` and :class:`datetime.date` are
+        serialized to :rfc:`822` strings. This is the same as the HTTP
+        date format.
+    -   :class:`uuid.UUID` is serialized to a string.
+    -   :class:`dataclasses.dataclass` is passed to
+        :func:`dataclasses.asdict`.
+    -   :class:`~markupsafe.Markup` (or any object with a ``__html__``
+        method) will call the ``__html__`` method to get a string.
 
-    In order to support more data types, override the :meth:`default`
-    method.
+    Assign a subclass of this to :attr:`flask.Flask.json_encoder` or
+    :attr:`flask.Blueprint.json_encoder` to override the default.
     """
 
     def default(self, o):
-        """Implement this method in a subclass such that it returns a
-        serializable object for ``o``, or calls the base implementation (to
-        raise a :exc:`TypeError`).
-
-        For example, to support arbitrary iterators, you could implement
-        default like this::
-
-            def default(self, o):
-                try:
-                    iterable = iter(o)
-                except TypeError:
-                    pass
-                else:
-                    return list(iterable)
-                return JSONEncoder.default(self, o)
+        """Convert ``o`` to a JSON serializable type. See
+        :meth:`json.JSONEncoder.default`. Python does not support
+        overriding how basic types like ``str`` or ``list`` are
+        serialized, they are handled before this method.
         """
         if isinstance(o, datetime):
             return http_date(o.utctimetuple())
@@ -61,10 +55,13 @@ class JSONEncoder(_json.JSONEncoder):
 
 
 class JSONDecoder(_json.JSONDecoder):
-    """The default JSON decoder.  This one does not change the behavior from
-    the default decoder.  Consult the :mod:`json` documentation
-    for more information.  This decoder is not only used for the load
-    functions of this module but also :attr:`~flask.Request`.
+    """The default JSON decoder.
+
+    This does not change any behavior from the built-in
+    :class:`json.JSONDecoder`.
+
+    Assign a subclass of this to :attr:`flask.Flask.json_decoder` or
+    :attr:`flask.Blueprint.json_decoder` to override the default.
     """
 
 
@@ -98,22 +95,20 @@ def _load_arg_defaults(kwargs, app=None):
 
 
 def dumps(obj, app=None, **kwargs):
-    """Serialize ``obj`` to a JSON-formatted string. If there is an
-    app context pushed, use the current app's configured encoder
-    (:attr:`~flask.Flask.json_encoder`), or fall back to the default
-    :class:`JSONEncoder`.
+    """Serialize an object to a string of JSON.
 
-    Takes the same arguments as the built-in :func:`json.dumps`, and
-    does some extra configuration based on the application.
+    Takes the same arguments as the built-in :func:`json.dumps`, with
+    some defaults from application configuration.
 
     :param obj: Object to serialize to JSON.
-    :param app: App instance to use to configure the JSON encoder.
-        Uses ``current_app`` if not given, and falls back to the default
-        encoder when not in an app context.
-    :param kwargs: Extra arguments passed to :func:`json.dumps`.
+    :param app: Use this app's config instead of the active app context
+        or defaults.
+    :param kwargs: Extra arguments passed to func:`json.dumps`.
+
+    .. versionchanged:: 2.0
+        ``encoding`` is deprecated and will be removed in 2.1.
 
     .. versionchanged:: 1.0.3
-
         ``app`` can be passed directly, rather than requiring an app
         context for configuration.
     """
@@ -135,7 +130,21 @@ def dumps(obj, app=None, **kwargs):
 
 
 def dump(obj, fp, app=None, **kwargs):
-    """Like :func:`dumps` but writes into a file object."""
+    """Serialize an object to JSON written to a file object.
+
+    Takes the same arguments as the built-in :func:`json.dump`, with
+    some defaults from application configuration.
+
+    :param obj: Object to serialize to JSON.
+    :param fp: File object to write JSON to.
+    :param app: Use this app's config instead of the active app context
+        or defaults.
+    :param kwargs: Extra arguments passed to func:`json.dump`.
+
+    .. versionchanged:: 2.0
+        Writing to a binary file, and the ``encoding`` argument, is
+        deprecated and will be removed in 2.1.
+    """
     _dump_arg_defaults(kwargs, app=app)
     encoding = kwargs.pop("encoding", None)
     show_warning = encoding is not None
@@ -158,22 +167,21 @@ def dump(obj, fp, app=None, **kwargs):
 
 
 def loads(s, app=None, **kwargs):
-    """Deserialize an object from a JSON-formatted string ``s``. If
-    there is an app context pushed, use the current app's configured
-    decoder (:attr:`~flask.Flask.json_decoder`), or fall back to the
-    default :class:`JSONDecoder`.
+    """Deserialize an object from a string of JSON.
 
-    Takes the same arguments as the built-in :func:`json.loads`, and
-    does some extra configuration based on the application.
+    Takes the same arguments as the built-in :func:`json.loads`, with
+    some defaults from application configuration.
 
     :param s: JSON string to deserialize.
-    :param app: App instance to use to configure the JSON decoder.
-        Uses ``current_app`` if not given, and falls back to the default
-        encoder when not in an app context.
-    :param kwargs: Extra arguments passed to :func:`json.dumps`.
+    :param app: Use this app's config instead of the active app context
+        or defaults.
+    :param kwargs: Extra arguments passed to func:`json.dump`.
+
+    .. versionchanged:: 2.0
+        ``encoding`` is deprecated and will be removed in 2.1. The data
+        must be a string or UTF-8 bytes.
 
     .. versionchanged:: 1.0.3
-
         ``app`` can be passed directly, rather than requiring an app
         context for configuration.
     """
@@ -195,7 +203,20 @@ def loads(s, app=None, **kwargs):
 
 
 def load(fp, app=None, **kwargs):
-    """Like :func:`loads` but reads from a file object."""
+    """Deserialize an object from JSON read from a file object.
+
+    Takes the same arguments as the built-in :func:`json.load`, with
+    some defaults from application configuration.
+
+    :param fp: File object to read JSON from.
+    :param app: Use this app's config instead of the active app context
+        or defaults.
+    :param kwargs: Extra arguments passed to func:`json.load`.
+
+    .. versionchanged:: 2.0
+        ``encoding`` is deprecated and will be removed in 2.1. The file
+        must be text mode, or binary mode with UTF-8 bytes.
+    """
     _load_arg_defaults(kwargs, app=app)
     encoding = kwargs.pop("encoding", None)
 
@@ -219,84 +240,80 @@ _htmlsafe_map = str.maketrans(
 
 
 def htmlsafe_dumps(obj, **kwargs):
-    """Works exactly like :func:`dumps` but is safe for use in ``<script>``
-    tags.  It accepts the same arguments and returns a JSON string.  Note that
-    this is available in templates through the ``|tojson`` filter which will
-    also mark the result as safe.  Due to how this function escapes certain
-    characters this is safe even if used outside of ``<script>`` tags.
+    """Serialize an object to a string of JSON, replacing HTML-unsafe
+    characters with Unicode escapes. Otherwise behaves the same as
+    :func:`dumps`.
 
-    The following characters are escaped in strings:
+    This is available in templates as the ``|tojson`` filter, which will
+    also mark the result with ``|safe``.
 
-    -   ``<``
-    -   ``>``
-    -   ``&``
-    -   ``'``
-
-    This makes it safe to embed such strings in any place in HTML with the
-    notable exception of double quoted attributes.  In that case single
-    quote your attributes or HTML escape it in addition.
+    The returned string is safe to render in HTML documents and
+    ``<script>`` tags. The exception is in HTML attributes that are
+    double quoted; either use single quotes or the ``|forceescape``
+    filter.
 
     .. versionchanged:: 0.10
-       This function's return value is now always safe for HTML usage, even
-       if outside of script tags or if used in XHTML.  This rule does not
-       hold true when using this function in HTML attributes that are double
-       quoted.  Always single quote attributes if you use the ``|tojson``
-       filter.  Alternatively use ``|tojson|forceescape``.
+        Single quotes are escaped, making this safe to use in HTML,
+        ``<script>`` tags, and single-quoted attributes without further
+        escaping.
     """
     return dumps(obj, **kwargs).translate(_htmlsafe_map)
 
 
 def htmlsafe_dump(obj, fp, **kwargs):
-    """Like :func:`htmlsafe_dumps` but writes into a file object."""
+    """Serialize an object to JSON written to a file object, replacing
+    HTML-unsafe characters with Unicode escapes. See
+    :func:`htmlsafe_dumps` and :func:`dumps`.
+    """
     fp.write(htmlsafe_dumps(obj, **kwargs))
 
 
 def jsonify(*args, **kwargs):
-    """This function wraps :func:`dumps` to add a few enhancements that make
-    life easier.  It turns the JSON output into a :class:`~flask.Response`
-    object with the :mimetype:`application/json` mimetype.  For convenience, it
-    also converts multiple arguments into an array or multiple keyword arguments
-    into a dict.  This means that both ``jsonify(1,2,3)`` and
-    ``jsonify([1,2,3])`` serialize to ``[1,2,3]``.
+    """Serialize data to JSON and wrap it in a :class:`~flask.Response`
+    with the :mimetype:`application/json` mimetype.
 
-    For clarity, the JSON serialization behavior has the following differences
-    from :func:`dumps`:
+    Uses :func:`dumps` to serialize the data, but ``args`` and
+    ``kwargs`` are treated as data rather than arguments to
+    :func:`json.dumps`.
 
-    1. Single argument: Passed straight through to :func:`dumps`.
-    2. Multiple arguments: Converted to an array before being passed to
-       :func:`dumps`.
-    3. Multiple keyword arguments: Converted to a dict before being passed to
-       :func:`dumps`.
-    4. Both args and kwargs: Behavior undefined and will throw an exception.
+    1.  Single argument: Treated as a single value.
+    2.  Multiple arguments: Treated as a list of values.
+        ``jsonify(1, 2, 3)`` is the same as ``jsonify([1, 2, 3])``.
+    3.  Keyword arguments: Treated as a dict of values.
+        ``jsonify(data=data, errors=errors)`` is the same as
+        ``jsonify({"data": data, "errors": errors})``.
+    4.  Passing both arguments and keyword arguments is not allowed as
+        it's not clear what should happen.
 
-    Example usage::
+    .. code-block:: python
 
         from flask import jsonify
 
-        @app.route('/_get_current_user')
+        @app.route("/users/me")
         def get_current_user():
-            return jsonify(username=g.user.username,
-                           email=g.user.email,
-                           id=g.user.id)
+            return jsonify(
+                username=g.user.username,
+                email=g.user.email,
+                id=g.user.id,
+            )
 
-    This will send a JSON response like this to the browser::
+    Will return a JSON response like this:
+
+    .. code-block:: javascript
 
         {
-            "username": "admin",
-            "email": "admin@localhost",
-            "id": 42
+          "username": "admin",
+          "email": "admin@localhost",
+          "id": 42
         }
 
+    The default output omits indents and spaces after separators. In
+    debug mode or if :data:`JSONIFY_PRETTYPRINT_REGULAR` is ``True``,
+    the output will be formatted to be easier to read.
 
     .. versionchanged:: 0.11
         Added support for serializing top-level arrays. This introduces
-        a security risk in ancient browsers. See :ref:`security-json`
-        for details.
-
-    This function's response will be pretty printed if the
-    ``JSONIFY_PRETTYPRINT_REGULAR`` config parameter is set to True or the
-    Flask app is running in debug mode. Compressed (not pretty) formatting
-    currently means no indents and no spaces after separators.
+        a security risk in ancient browsers. See :ref:`security-json`.
 
     .. versionadded:: 0.2
     """
diff --git a/src/flask/json/tag.py b/src/flask/json/tag.py
index 7e762426..d3c29adb 100644
--- a/src/flask/json/tag.py
+++ b/src/flask/json/tag.py
@@ -45,7 +45,7 @@ from base64 import b64encode
 from datetime import datetime
 from uuid import UUID
 
-from jinja2 import Markup
+from markupsafe import Markup
 from werkzeug.http import http_date
 from werkzeug.http import parse_date
 
@@ -167,9 +167,9 @@ class TagBytes(JSONTag):
 
 
 class TagMarkup(JSONTag):
-    """Serialize anything matching the :class:`~flask.Markup` API by
+    """Serialize anything matching the :class:`~markupsafe.Markup` API by
     having a ``__html__`` method to the result of that method. Always
-    deserializes to an instance of :class:`~flask.Markup`."""
+    deserializes to an instance of :class:`~markupsafe.Markup`."""
 
     __slots__ = ()
     key = " m"
@@ -222,7 +222,7 @@ class TaggedJSONSerializer:
     * :class:`dict`
     * :class:`tuple`
     * :class:`bytes`
-    * :class:`~flask.Markup`
+    * :class:`~markupsafe.Markup`
     * :class:`~uuid.UUID`
     * :class:`~datetime.datetime`
     """