diff --git a/.doctor-rst.yaml b/.doctor-rst.yaml
index 61b56614a29..388147a8281 100644
--- a/.doctor-rst.yaml
+++ b/.doctor-rst.yaml
@@ -101,3 +101,4 @@ whitelist:
         - 'provides a ``loginUser()`` method to simulate logging in in your functional'
         - '.. code-block:: twig'
         - '.. versionadded:: 3.6' # MonologBundle
+        - '// bin/console'
diff --git a/components/runtime.rst b/components/runtime.rst
new file mode 100644
index 00000000000..dc745adb5c6
--- /dev/null
+++ b/components/runtime.rst
@@ -0,0 +1,490 @@
+.. index::
+   single: Runtime
+   single: Components; Runtime
+
+The Runtime Component
+======================
+
+    The Runtime Component decouples the bootstrapping logic from any global state
+    to make sure the application can run with runtimes like PHP-FPM, ReactPHP,
+    Swoole, etc. without any changes.
+
+.. versionadded:: 5.3
+
+    The Runtime component was introduced in Symfony 5.3.
+
+Installation
+------------
+
+.. code-block:: terminal
+
+    $ composer require symfony/runtime
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+The Runtime component abstracts most bootstrapping logic as so-called
+*runtimes*, allowing you to write front-controllers in a generic way.
+For instance, the Runtime component allows Symfony's ``public/index.php``
+to look like this::
+
+    <?php
+    // public/index.php
+    use App\Kernel;
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    return function (array $context) {
+        return new Kernel($context['APP_ENV'], (bool) $context['APP_DEBUG']);
+    };
+
+So how does this front-controller work? At first, the special
+``autoload_runtime.php`` is automatically created by the Composer plugin in
+the component. This file runs the following logic:
+
+#. It instantiates a :class:`Symfony\\Component\\Runtime\\RuntimeInterface`;
+#. The callable (returned by ``public/index.php``) is passed to the Runtime, whose job
+   is to resolve the arguments (in this example: ``array $content``);
+#. Then, this callable is called to get the application (``App\Kernel``);
+#. At last, the Runtime is used to run the application (i.e. calling
+   ``$kernel->handle(Request::createFromGlobals())->send()``).
+
+To make a console application, the bootstrap code would look like::
+
+    #!/usr/bin/env php
+    <?php
+    // bin/console
+
+    use App\Kernel;
+    use Symfony\Bundle\FrameworkBundle\Console\Application;
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    return function (array $context) {
+        $kernel = new Kernel($context['APP_ENV'], (bool) $context['APP_DEBUG']);
+
+        // returning an "Application" makes the Runtime run a Console
+        // application instead of the HTTP Kernel
+        return new Application($kernel);
+    };
+
+Selecting Runtimes
+------------------
+
+The default Runtime is :class:`Symfony\\Component\\Runtime\\SymfonyRuntime`. It
+works excellent on most applications running with a webserver using PHP-FPM like
+Nginx or Apache.
+
+The component also provides a :class:`Symfony\\Component\\Runtime\\GenericRuntime`,
+which uses PHP's ``$_SERVER``, ``$_POST``, ``$_GET``, ``$_FILES`` and
+``$_SESSION`` superglobals. You may also use a custom Runtime (e.g. to
+integrate with Swoole or AWS Lambda).
+
+Use the ``APP_RUNTIME`` environment variable or by specifying the
+``extra.runtime.class`` in ``composer.json`` to change the Runtime class:
+
+.. configuration-block::
+
+    .. code-block:: json
+
+        {
+            "require": {
+                "...": "..."
+            },
+            "extra": {
+                "runtime": {
+                    "class": "Symfony\\Component\\Runtime\\GenericRuntime"
+                }
+            }
+        }
+
+    .. code-block:: env
+
+        APP_RUNTIME="Symfony\\Component\\Runtime\\GenericRuntime"
+
+Using the Runtime
+-----------------
+
+A Runtime is responsible for passing arguments into the closure and run the
+application returned by the closure. The :class:`Symfony\\Component\\Runtime\\SymfonyRuntime` and
+:class:`Symfony\\Component\\Runtime\\GenericRuntime` supports a number of
+arguments and different applications that you can use in your
+front-controllers.
+
+Resolvable Arguments
+~~~~~~~~~~~~~~~~~~~~
+
+The closure returned from the front-controller may have zero or more arguments::
+
+    <?php
+    // public/index.php
+    use Symfony\Component\Console\Input\InputInterface;
+    use Symfony\Component\Console\Output\OutputInterface;
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    return function (InputInterface $input, OutputInterface $output) {
+        // ...
+    };
+
+The following arguments are supported by the ``SymfonyRuntime``:
+
+:class:`Symfony\\Component\\HttpFoundation\\Request`
+    A request created from globals.
+
+:class:`Symfony\\Component\\Console\\Input\\InputInterface`
+    An input to read options and arguments.
+
+:class:`Symfony\\Component\\Console\\Output\\OutputInterface`
+    Console output to print to the CLI with style.
+
+:class:`Symfony\\Component\\Console\\Application`
+    An application for creating CLI applications.
+
+:class:`Symfony\\Component\\Command\\Command`
+    For creating one line command CLI applications (using
+    ``Command::setCode()``).
+
+And these arguments are supported by both the ``SymfonyRuntime`` and
+``GenerGenericRuntime`` (both type and variable name are important):
+
+``array $context``
+    This is the same as ``$_SERVER`` + ``$_ENV``.
+
+``array $argv``
+    The arguments passed to the command (same as ``$_SERVER['argv']``).
+
+``array $request``
+    With keys ``query``, ``body``, ``files`` and ``session``.
+
+Resolvable Applications
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The application returned by the closure below is a Symfony Kernel. However,
+a number of different applications are supported::
+
+    <?php
+    // public/index.php
+    use App\Kernel;
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    return function () {
+        return new Kernel('prod', false);
+    };
+
+The ``SymfonyRuntime`` can handle these applications:
+
+:class:`Symfony\\Component\\HttpKernel\\HttpKernelInterface`
+    The application will be run with :class:`Symfony\\Component\\Runtime\\Runner\\Symfony\\HttpKernelRunner``
+    like a "standard" Symfony application.
+
+:class:`Symfony\\Component\\HttpFoundation\\Response`
+    The Response will be printed by
+    :class:`Symfony\\Component\\Runtime\\Runner\\Symfony\\ResponseRunner``::
+
+        <?php
+        // public/index.php
+        use Symfony\Component\HttpFoundation\Response;
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function () {
+            return new Response('Hello world');
+        };
+
+:class:`Symfony\\Component\\Console\\Command\\Command`
+    To write single command applications. This will use the
+    :class:`Symfony\\Component\\Runtime\\Runner\\Symfony\\ConsoleApplicationRunner``::
+
+        <?php
+
+        use Symfony\Component\Console\Command\Command;
+        use Symfony\Component\Console\Input\InputInterface;
+        use Symfony\Component\Console\Output\OutputInterface;
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function (Command $command) {
+            $command->setCode(function (InputInterface $input, OutputInterface $output) {
+                $output->write('Hello World');
+            });
+
+            return $command;
+        };
+
+:class:`Symfony\\Component\\Console\\Application`
+    Useful with console applications with more than one command. This will use the
+    :class:`Symfony\\Component\\Runtime\\Runner\\Symfony\\ConsoleApplicationRunner``::
+
+        <?php
+
+        use Symfony\Component\Console\Application;
+        use Symfony\Component\Console\Command\Command;
+        use Symfony\Component\Console\Input\InputInterface;
+        use Symfony\Component\Console\Output\OutputInterface;
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function (array $context) {
+            $command = new Command('hello');
+            $command->setCode(function (InputInterface $input, OutputInterface $output) {
+                $output->write('Hello World');
+            });
+
+            $app = new Application();
+            $app->add($command);
+            $app->setDefaultCommand('hello', true);
+
+            return $app;
+        };
+
+The ``GenericRuntime`` and ``SymfonyRuntime`` also support these generic
+applications:
+
+:class:`Symfony\\Component\\Runtime\\RunnerInterface`
+    The ``RunnerInterface`` is a way to use a custom application with the
+    generic Runtime::
+
+        <?php
+        // public/index.php
+        use Symfony\Component\Runtime\RunnerInterface;
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function () {
+            return new class implements RunnerInterface {
+                public function run(): int
+                {
+                    echo 'Hello World';
+
+                    return 0;
+                }
+            };
+        };
+
+``callable``
+    Your "application" can also be a ``callable``. The first callable will return
+    the "application" and the second callable is the "application" itself::
+
+        <?php
+        // public/index.php
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function () {
+            $app = function() {
+                echo 'Hello World';
+
+                return 0;
+            };
+
+            return $app;
+        };
+
+``void``
+    If the callable doesn't return anything, the ``SymfonyRuntime`` will assume
+    everything is fine::
+
+        <?php
+
+        require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+        return function () {
+            echo 'Hello world';
+        };
+
+Using Options
+~~~~~~~~~~~~~
+
+Some behavior of the Runtimes can be modified through runtime options. They
+can be set using the ``APP_RUNTIME_OPTIONS`` environment variable::
+
+    <?php
+
+    $_SERVER['APP_RUNTIME_OPTIONS'] = [
+        'project_dir' => '/var/task',
+    ];
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    // ...
+
+You can also configure ``extra.runtime.options`` in ``composer.json``:
+
+.. code-block:: json
+
+    {
+        "require": {
+            "...": "..."
+        },
+        "extra": {
+            "runtime": {
+                "options": {
+                    "project_dir": "/var/task"
+                }
+            }
+        }
+    }
+
+The following options are supported by the ``SymfonyRuntime``:
+
+``env`` (default: ``APP_ENV`` environment variable, or ``"dev"``)
+    To define the name of the environment the app runs in.
+``disable_dotenv`` (default: ``false``)
+    To disable looking for ``.env`` files.
+``dotenv_path`` (default: ``.env``)
+    To define the path of dot-env files.
+``use_putenv``
+    To tell Dotenv to set env vars using ``putenv()`` (NOT RECOMMENDED).
+``prod_envs`` (default: ``["prod"]``)
+    To define the names of the production envs.
+``test_envs`` (default: ``["test"]``)
+    To define the names of the test envs.
+
+Besides these, the ``GenericRuntime`` and ``SymfonyRuntime`` also support
+these options:
+
+``debug`` (default: ``APP_DEBUG`` environment variable, or ``true``)
+    Toggles displaying errors.
+``runtimes``
+    Maps "application types" to a ``GenericRuntime`` implementation that
+    knows how to deal with each of them.
+``error_handler`` (default: :class:`Symfony\\Component\\Runtime\\Internal\\BasicErrorHandler` or :class:`Symfony\\Component\\Runtime\\Internal\\SymfonyErrorHandler` for ``SymfonyRuntime``)
+    Defines the class to use to handle PHP errors.
+
+Create Your Own Runtime
+-----------------------
+
+This is an advanced topic that describes the internals of the Runtime component.
+
+Using the Runtime component will benefit maintainers because the bootstrap
+logic could be versioned as a part of a normal package. If the application
+author decides to use this component, the package maintainer of the Runtime
+class will have more control and can fix bugs and add features.
+
+.. note::
+
+    Before Symfony 5.3, the Symfony boostrap logic was part of a Flex recipe.
+    Since recipes are rarely updated by users, bug patches would rarely be
+    installed.
+
+The Runtime component is designed to be totally generic and able to run any
+application outside of the global state in 6 steps:
+
+#. The main entry point returns a *callable* (the "app") that wraps the application;
+#. The *app callable* is passed to ``RuntimeInterface::getResolver()``, which returns
+   a :class:`Symfony\\Component\\Runtime\\ResolverInterface`. This resolver returns
+   an array with the app callable (or something that decorates this callable) at
+   index 0 and all its resolved arguments at index 1.
+#. The *app callable* is invoked with its arguments, it will return an object that
+   represents the application.
+#. This *application object* is passed to ``RuntimeInterface::getRunner()``, which
+   returns a :class:`Symfony\\Component\\Runtime\\RunnerInterface`: an instance
+   that knows how to "run" the appliction object.
+#. The ``RunnerInterface::run(object $application)`` is called and it returns the
+   exit status code as `int`.
+#. The PHP engine is exited with this status code.
+
+When creating a new runtime, there are two things to consider: First, what arguments
+will the end user use? Second, what will the user's application look like?
+
+For instance, imagine you want to create a runtime for `ReactPHP`_:
+
+**What arguments will the end user use?**
+
+For a generic ReactPHP application, no special arguments are
+typically required. This means that you can use the
+:class:`Symfony\\Component\\Runtime\\GenericRuntime`.
+
+**What will the user's application look like?**
+
+There is also no typical React application, so you might want to rely on
+the `PSR-15`_ interfaces for HTTP request handling.
+
+However, a ReactPHP application will need some special logic to *run*. That logic
+is added in a new class implementing :class:`Symfony\\Component\\Runtime\\RunnerInterface`::
+
+    use Psr\Http\Message\ServerRequestInterface;
+    use Psr\Http\Server\RequestHandlerInterface;
+    use React\EventLoop\Factory as ReactFactory;
+    use React\Http\Server as ReactHttpServer;
+    use React\Socket\Server as ReactSocketServer;
+    use Symfony\Component\Runtime\RunnerInterface;
+
+    class ReactPHPRunner implements RunnerInterface
+    {
+        private $application;
+        private $port;
+
+        public function __construct(RequestHandlerInterface $application, int $port)
+        {
+            $this->application = $application;
+            $this->port = $port;
+        }
+
+        public function run(): int
+        {
+            $application = $this->application;
+            $loop = ReactFactory::create();
+
+            // configure ReactPHP to correctly handle the PSR-15 application
+            $server = new ReactHttpServer(
+                $loop,
+                function (ServerRequestInterface $request) use ($application) {
+                    return $application->handle($request);
+                }
+            );
+
+            // start the ReactPHP server
+            $socket = new ReactSocketServer($this->port, $loop);
+            $server->listen($socket);
+
+            $loop->run();
+
+            return 0;
+        }
+    }
+
+By extending the ``GenericRuntime``, you make sure that the application is
+always using this ``ReactPHPRunner``::
+
+    use Symfony\Component\Runtime\GenericRuntime;
+    use Symfony\Component\Runtime\RunnerInterface;
+
+    class ReactPHPRuntime extends GenericRuntime
+    {
+        private $port;
+
+        public function __construct(array $options)
+        {
+            $this->port = $options['port'] ?? 8080;
+            parent::__construct($options);
+        }
+
+        public function getRunner(?object $application): RunnerInterface
+        {
+            if ($application instanceof RequestHandlerInterface) {
+                return new ReactPHPRunner($application, $this->port);
+            }
+
+            // if it's not a PSR-15 application, use the GenericRuntime to
+            // run the application (see "Resolvable Applications" above)
+            return parent::getRunner($application);
+        }
+    }
+
+The end user will now be able to create front controller like::
+
+    <?php
+
+    require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+    return function (array $context) {
+        return new SomeCustomPsr15Application();
+    };
+
+.. _ReactPHP: https://reactphp.org/
+.. _`PSR-15`: https://www.php-fig.org/psr/psr-15/