diff --git a/wp-includes/rest-api.php b/wp-includes/rest-api.php
index 28187154e7fc..b2df5ad62d71 100644
--- a/wp-includes/rest-api.php
+++ b/wp-includes/rest-api.php
@@ -301,6 +301,10 @@ function create_initial_rest_routes() {
 	$controller = new WP_REST_Block_Types_Controller();
 	$controller->register_routes();
 
+	// Global Styles.
+	$controller = new WP_REST_Global_Styles_Controller;
+	$controller->register_routes();
+
 	// Settings.
 	$controller = new WP_REST_Settings_Controller;
 	$controller->register_routes();
diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-global-styles-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-global-styles-controller.php
new file mode 100644
index 000000000000..c97acdbd2e38
--- /dev/null
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-global-styles-controller.php
@@ -0,0 +1,416 @@
+<?php
+/**
+ * REST API: WP_REST_Global_Styles_Controller class
+ *
+ * @package    WordPress
+ * @subpackage REST_API
+ * @since 5.9.0
+ */
+
+/**
+ * Base Global Styles REST API Controller.
+ */
+class WP_REST_Global_Styles_Controller extends WP_REST_Controller {
+	/**
+	 * Constructor.
+	 * @since 5.9.0
+	 */
+	public function __construct() {
+		$this->namespace = 'wp/v2';
+		$this->rest_base = 'global-styles';
+	}
+
+	/**
+	 * Registers the controllers routes.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @return void
+	 */
+	public function register_routes() {
+		// List themes global styles.
+		register_rest_route(
+			$this->namespace,
+			'/' . $this->rest_base . '/themes/(?P<stylesheet>[^.\/]+(?:\/[^.\/]+)?)',
+			array(
+				array(
+					'methods'             => WP_REST_Server::READABLE,
+					'callback'            => array( $this, 'get_theme_item' ),
+					'permission_callback' => array( $this, 'get_theme_item_permissions_check' ),
+					'args'                => array(
+						'stylesheet' => array(
+							'description' => __( 'The theme identifier' ),
+							'type'        => 'string',
+						),
+					),
+				),
+			)
+		);
+
+		// Lists/updates a single gloval style variation based on the given id.
+		register_rest_route(
+			$this->namespace,
+			'/' . $this->rest_base . '/(?P<id>[\/\w-]+)',
+			array(
+				array(
+					'methods'             => WP_REST_Server::READABLE,
+					'callback'            => array( $this, 'get_item' ),
+					'permission_callback' => array( $this, 'get_item_permissions_check' ),
+					'args'                => array(
+						'id' => array(
+							'description' => __( 'The id of a template' ),
+							'type'        => 'string',
+						),
+					),
+				),
+				array(
+					'methods'             => WP_REST_Server::EDITABLE,
+					'callback'            => array( $this, 'update_item' ),
+					'permission_callback' => array( $this, 'update_item_permissions_check' ),
+					'args'                => $this->get_endpoint_args_for_item_schema( WP_REST_Server::EDITABLE ),
+				),
+				'schema' => array( $this, 'get_public_item_schema' ),
+			)
+		);
+	}
+
+	/**
+	 * Checks if the user has permissions to make the request.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @return true|WP_Error True if the request has read access, WP_Error object otherwise.
+	 */
+	protected function permissions_check() {
+		// Verify if the current user has edit_theme_options capability.
+		// This capability is required to edit/view/delete templates.
+		if ( ! current_user_can( 'edit_theme_options' ) ) {
+			return new WP_Error(
+				'rest_cannot_manage_global_styles',
+				__( 'Sorry, you are not allowed to access the global styles on this site.' ),
+				array(
+					'status' => rest_authorization_required_code(),
+				)
+			);
+		}
+
+		return true;
+	}
+
+	/**
+	 * Checks if a given request has access to read a single global styles config.
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has read access for the item, WP_Error object otherwise.
+	 */
+	public function get_item_permissions_check( $request ) {
+		return $this->permissions_check( $request );
+	}
+
+	/**
+	 * Returns the given global styles config.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request The request instance.
+	 *
+	 * @return WP_REST_Response|WP_Error
+	 */
+	public function get_item( $request ) {
+		$post = get_post( $request['id'] );
+		if ( ! $post || 'wp_global_styles' !== $post->post_type ) {
+			return new WP_Error( 'rest_global_styles_not_found', __( 'No global styles config exist with that id.' ), array( 'status' => 404 ) );
+		}
+
+		return $this->prepare_item_for_response( $post, $request );
+	}
+
+	/**
+	 * Checks if a given request has access to write a single global styles config.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has write access for the item, WP_Error object otherwise.
+	 */
+	public function update_item_permissions_check( $request ) {
+		return $this->permissions_check( $request );
+	}
+
+	/**
+	 * Updates a single global style config.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
+	 */
+	public function update_item( $request ) {
+		$post = get_post( $request['id'] );
+		if ( ! $post || 'wp_global_styles' !== $post->post_type ) {
+			return new WP_Error( 'rest_global_styles_not_found', __( 'No global styles config exist with that id.' ), array( 'status' => 404 ) );
+		}
+
+		$changes = $this->prepare_item_for_database( $request );
+		$result  = wp_update_post( wp_slash( (array) $changes ), true );
+		if ( is_wp_error( $result ) ) {
+			return $result;
+		}
+
+		$post          = get_post( $request['id'] );
+		$fields_update = $this->update_additional_fields_for_object( $post, $request );
+		if ( is_wp_error( $fields_update ) ) {
+			return $fields_update;
+		}
+
+		return $this->prepare_item_for_response(
+			get_post( $request['id'] ),
+			$request
+		);
+	}
+
+	/**
+	 * Prepares a single global styles config for update.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request Request object.
+	 * @return stdClass Changes to pass to wp_update_post.
+	 */
+	protected function prepare_item_for_database( $request ) {
+		$changes     = new stdClass();
+		$changes->ID = $request['id'];
+
+		$post            = get_post( $request['id'] );
+		$existing_config = array();
+		if ( $post ) {
+			$existing_config     = json_decode( $post->post_content, true );
+			$json_decoding_error = json_last_error();
+			if ( JSON_ERROR_NONE !== $json_decoding_error || ! isset( $existing_config['isGlobalStylesUserThemeJSON'] ) ||
+				! $existing_config['isGlobalStylesUserThemeJSON'] ) {
+				$existing_config = array();
+			}
+		}
+
+		if ( isset( $request['styles'] ) || isset( $request['settings'] ) ) {
+			$config = array();
+			if ( isset( $request['styles'] ) ) {
+				$config['styles'] = $request['styles'];
+			} elseif ( isset( $existing_config['styles'] ) ) {
+				$config['styles'] = $existing_config['styles'];
+			}
+			if ( isset( $request['settings'] ) ) {
+				$config['settings'] = $request['settings'];
+			} elseif ( isset( $existing_config['settings'] ) ) {
+				$config['settings'] = $existing_config['settings'];
+			}
+			$config['isGlobalStylesUserThemeJSON'] = true;
+			$config['version']                     = WP_Theme_JSON::LATEST_SCHEMA;
+			$changes->post_content                 = wp_json_encode( $config );
+		}
+
+		// Post title.
+		if ( isset( $request['title'] ) ) {
+			if ( is_string( $request['title'] ) ) {
+				$changes->post_title = $request['title'];
+			} elseif ( ! empty( $request['title']['raw'] ) ) {
+				$changes->post_title = $request['title']['raw'];
+			}
+		}
+
+		return $changes;
+	}
+
+	/**
+	 * Prepare a global styles config output for response.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_Post         $post    Global Styles post object.
+	 * @param WP_REST_Request $request Request object.
+	 *
+	 * @return WP_REST_Response $data
+	 */
+	public function prepare_item_for_response( $post, $request ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable
+		$config                           = json_decode( $post->post_content, true );
+		$is_global_styles_user_theme_json = isset( $config['isGlobalStylesUserThemeJSON'] ) && true === $config['isGlobalStylesUserThemeJSON'];
+		$result                           = array(
+			'id'       => $post->ID,
+			'settings' => ! empty( $config['settings'] ) && $is_global_styles_user_theme_json ? $config['settings'] : new stdClass(),
+			'styles'   => ! empty( $config['styles'] ) && $is_global_styles_user_theme_json ? $config['styles'] : new stdClass(),
+			'title'    => array(
+				'raw'      => $post->post_title,
+				'rendered' => get_the_title( $post ),
+			),
+		);
+		$result                           = $this->add_additional_fields_to_object( $result, $request );
+		$response                         = rest_ensure_response( $result );
+		$links                            = $this->prepare_links( $post->id );
+		$response->add_links( $links );
+		if ( ! empty( $links['self']['href'] ) ) {
+			$actions = $this->get_available_actions();
+			$self    = $links['self']['href'];
+			foreach ( $actions as $rel ) {
+				$response->add_link( $rel, $self );
+			}
+		}
+
+		return $response;
+	}
+
+
+	/**
+	 * Prepares links for the request.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param integer $id ID.
+	 * @return array Links for the given post.
+	 */
+	protected function prepare_links( $id ) {
+		$base = sprintf( '%s/%s', $this->namespace, $this->rest_base );
+
+		$links = array(
+			'self'       => array(
+				'href' => rest_url( trailingslashit( $base ) . $id ),
+			),
+			'collection' => array(
+				'href' => rest_url( $base ),
+			),
+		);
+
+		return $links;
+	}
+
+	/**
+	 * Get the link relations available for the post and current user.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @return array List of link relations.
+	 */
+	protected function get_available_actions() {
+		$rels = array();
+
+		$post_type = get_post_type_object( 'wp_global_styles' );
+		if ( current_user_can( $post_type->cap->publish_posts ) ) {
+			$rels[] = 'https://api.w.org/action-publish';
+		}
+
+		return $rels;
+	}
+
+	/**
+	 * Retrieves the query params for the global styles collection.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @return array Collection parameters.
+	 */
+	public function get_collection_params() {
+		return array();
+	}
+
+	/**
+	 * Retrieves the global styles type' schema, conforming to JSON Schema.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @return array Item schema data.
+	 */
+	public function get_item_schema() {
+		if ( $this->schema ) {
+			return $this->add_additional_fields_schema( $this->schema );
+		}
+
+		$schema = array(
+			'$schema'    => 'http://json-schema.org/draft-04/schema#',
+			'title'      => 'wp_global_styles',
+			'type'       => 'object',
+			'properties' => array(
+				'id'       => array(
+					'description' => __( 'ID of global styles config.' ),
+					'type'        => 'string',
+					'context'     => array( 'embed', 'view', 'edit' ),
+					'readonly'    => true,
+				),
+				'styles'   => array(
+					'description' => __( 'Global styles.' ),
+					'type'        => array( 'object' ),
+					'context'     => array( 'view', 'edit' ),
+				),
+				'settings' => array(
+					'description' => __( 'Global settings.' ),
+					'type'        => array( 'object' ),
+					'context'     => array( 'view', 'edit' ),
+				),
+				'title'    => array(
+					'description' => __( 'Title of the global styles variation.' ),
+					'type'        => array( 'object', 'string' ),
+					'default'     => '',
+					'context'     => array( 'embed', 'view', 'edit' ),
+					'properties'  => array(
+						'raw'      => array(
+							'description' => __( 'Title for the global styles variation, as it exists in the database.' ),
+							'type'        => 'string',
+							'context'     => array( 'view', 'edit', 'embed' ),
+						),
+						'rendered' => array(
+							'description' => __( 'HTML title for the post, transformed for display.' ),
+							'type'        => 'string',
+							'context'     => array( 'view', 'edit', 'embed' ),
+							'readonly'    => true,
+						),
+					),
+				),
+			),
+		);
+
+		$this->schema = $schema;
+
+		return $this->add_additional_fields_schema( $this->schema );
+	}
+
+	/**
+	 * Checks if a given request has access to read a single theme global styles config.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has read access for the item, WP_Error object otherwise.
+	 */
+	public function get_theme_item_permissions_check( $request ) {
+		return $this->permissions_check( $request );
+	}
+
+	/**
+	 * Returns the given theme global styles config.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_REST_Request $request The request instance.
+	 *
+	 * @return WP_REST_Response|WP_Error
+	 */
+	public function get_theme_item( $request ) {
+		if ( wp_get_theme()->get_stylesheet() !== $request['stylesheet'] ) {
+			// This endpoint only supports the active theme for now.
+			return new WP_Error(
+				'rest_theme_not_found',
+				__( 'Theme not found.' ),
+				array( 'status' => 404 )
+			);
+		}
+
+		$theme    = WP_Theme_JSON_Resolver::get_merged_data( 'theme' );
+		$styles   = $theme->get_raw_data()['styles'];
+		$settings = $theme->get_settings();
+		$result   = array(
+			'settings' => $settings,
+			'styles'   => $styles,
+		);
+		$response = rest_ensure_response( $result );
+
+		return $response;
+	}
+}
diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
index b34bc317e185..b49810d1e39d 100644
--- a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
@@ -316,6 +316,35 @@ public function prepare_item_for_response( $item, $request ) {
 
 		$response->add_links( $this->prepare_links( $theme ) );
 
+		if ( $theme->get_stylesheet() === wp_get_theme()->get_stylesheet() ) {
+			// This creates a record for the current theme if not existent.
+			$id = WP_Theme_JSON_Resolver::get_user_custom_post_type_id();
+		} else {
+			$wp_query_args       = array(
+				'post_status'    => 'publish',
+				'post_type'      => 'wp_global_styles',
+				'posts_per_page' => 1,
+				'no_found_rows'  => true,
+				'fields'         => 'ids',
+				'tax_query'      => array(
+					array(
+						'taxonomy' => 'wp_theme',
+						'field'    => 'name',
+						'terms'    => $theme->get_stylesheet(),
+					),
+				),
+			);
+			$global_styles_query = new WP_Query( $wp_query_args );
+			$id                  = ! empty( $global_styles_query->posts ) ? array_shift( $global_styles_query->posts ) : null;
+		}
+
+		if ( $id ) {
+			$response->add_link(
+				'https://api.w.org/user-global-styles',
+				rest_url( 'wp/v2/global-styles/' . $id )
+			);
+		}
+
 		/**
 		 * Filters theme data returned from the REST API.
 		 *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index dd3ba9e5c506..ba768ecce834 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52050';
+$wp_version = '5.9-alpha-52051';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-settings.php b/wp-settings.php
index d2778166c180..d3ce78c31dff 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -254,6 +254,7 @@
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-controller.php';
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-posts-controller.php';
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-attachments-controller.php';
+require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-global-styles-controller.php';
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-post-types-controller.php';
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-post-statuses-controller.php';
 require ABSPATH . WPINC . '/rest-api/endpoints/class-wp-rest-revisions-controller.php';