diff --git a/wp-includes/block-editor.php b/wp-includes/block-editor.php
index f1ec5d2d1acf..814433f27867 100644
--- a/wp-includes/block-editor.php
+++ b/wp-includes/block-editor.php
@@ -243,6 +243,50 @@ function get_block_editor_settings( $editor_name, $custom_settings = array() ) {
 		$custom_settings
 	);
 
+	$editor_settings['__experimentalFeatures'] = WP_Theme_JSON_Resolver::get_merged_data( $editor_settings )->get_settings();
+
+	// These settings may need to be updated based on data coming from theme.json sources.
+	if ( isset( $editor_settings['__experimentalFeatures']['color']['palette'] ) ) {
+		$editor_settings['colors'] = $editor_settings['__experimentalFeatures']['color']['palette'];
+		unset( $editor_settings['__experimentalFeatures']['color']['palette'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['color']['gradients'] ) ) {
+		$editor_settings['gradients'] = $editor_settings['__experimentalFeatures']['color']['gradients'];
+		unset( $editor_settings['__experimentalFeatures']['color']['gradients'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['color']['custom'] ) ) {
+		$editor_settings['disableCustomColors'] = $editor_settings['__experimentalFeatures']['color']['custom'];
+		unset( $editor_settings['__experimentalFeatures']['color']['custom'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['color']['customGradient'] ) ) {
+		$editor_settings['disableCustomGradients'] = $editor_settings['__experimentalFeatures']['color']['customGradient'];
+		unset( $editor_settings['__experimentalFeatures']['color']['customGradient'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['typography']['fontSizes'] ) ) {
+		$editor_settings['fontSizes'] = $editor_settings['__experimentalFeatures']['typography']['fontSizes'];
+		unset( $editor_settings['__experimentalFeatures']['typography']['fontSizes'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['typography']['customFontSize'] ) ) {
+		$editor_settings['disableCustomFontSizes'] = $editor_settings['__experimentalFeatures']['typography']['customFontSize'];
+		unset( $editor_settings['__experimentalFeatures']['typography']['customFontSize'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['typography']['customLineHeight'] ) ) {
+		$editor_settings['enableCustomLineHeight'] = $editor_settings['__experimentalFeatures']['typography']['customLineHeight'];
+		unset( $editor_settings['__experimentalFeatures']['typography']['customLineHeight'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['spacing']['units'] ) ) {
+		if ( ! is_array( $editor_settings['__experimentalFeatures']['spacing']['units'] ) ) {
+			$editor_settings['enableCustomUnits'] = false;
+		} else {
+			$editor_settings['enableCustomUnits'] = count( $editor_settings['__experimentalFeatures']['spacing']['units'] ) > 0;
+		}
+		unset( $editor_settings['__experimentalFeatures']['spacing']['units'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['spacing']['customPadding'] ) ) {
+		$editor_settings['enableCustomSpacing'] = $editor_settings['__experimentalFeatures']['spacing']['customPadding'];
+		unset( $editor_settings['__experimentalFeatures']['spacing']['customPadding'] );
+	}
+
 	/**
 	 * Filters the settings to pass to the block editor for all editor type.
 	 *
diff --git a/wp-includes/class-wp-theme-json-resolver.php b/wp-includes/class-wp-theme-json-resolver.php
new file mode 100644
index 000000000000..87e2fa4bf150
--- /dev/null
+++ b/wp-includes/class-wp-theme-json-resolver.php
@@ -0,0 +1,362 @@
+<?php
+/**
+ * Process the different data sources for site-level
+ * config and offers and API to work with them.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Class that abstracts the processing
+ * of the different data sources.
+ *
+ * @access private
+ */
+class WP_Theme_JSON_Resolver {
+
+	/**
+	 * Container for data coming from core.
+	 *
+	 * @var WP_Theme_JSON
+	 */
+	private static $core = null;
+
+	/**
+	 * Container for data coming from the theme.
+	 *
+	 * @var WP_Theme_JSON
+	 */
+	private static $theme = null;
+
+	/**
+	 * Whether or not the theme supports theme.json.
+	 *
+	 * @var boolean
+	 */
+	private static $theme_has_support = null;
+
+	/**
+	 * Structure to hold i18n metadata.
+	 *
+	 * @var Array
+	 */
+	private static $theme_json_i18n = null;
+
+	/**
+	 * Processes a file that adheres to the theme.json
+	 * schema and returns an array with its contents,
+	 * or a void array if none found.
+	 *
+	 * @param string $file_path Path to file. Empty if no file.
+	 *
+	 * @return array Contents that adhere to the theme.json schema.
+	 */
+	private static function read_json_file( $file_path ) {
+		$config = array();
+		if ( $file_path ) {
+			$decoded_file = json_decode(
+				file_get_contents( $file_path ),
+				true
+			);
+
+			$json_decoding_error = json_last_error();
+			if ( JSON_ERROR_NONE !== $json_decoding_error ) {
+				error_log( 'Error when decoding file schema: ' . json_last_error_msg() );
+				return $config;
+			}
+
+			if ( is_array( $decoded_file ) ) {
+				$config = $decoded_file;
+			}
+		}
+		return $config;
+	}
+
+	/**
+	 * Converts a tree as in i18n-theme.json into a linear array
+	 * containing metadata to translate a theme.json file.
+	 *
+	 * For example, given this input:
+	 *
+	 * {
+	 *   "settings": {
+	 *     "*": {
+	 *       "typography": {
+	 *         "fontSizes": [ { "name": "Font size name" } ],
+	 *         "fontStyles": [ { "name": "Font size name" } ]
+	 *       }
+	 *     }
+	 *   }
+	 * }
+	 *
+	 * will return this output:
+	 *
+	 * [
+	 *   0 => [
+	 *     'path'    => [ 'settings', '*', 'typography', 'fontSizes' ],
+	 *     'key'     => 'name',
+	 *     'context' => 'Font size name'
+	 *   ],
+	 *   1 => [
+	 *     'path'    => [ 'settings', '*', 'typography', 'fontStyles' ],
+	 *     'key'     => 'name',
+	 *     'context' => 'Font style name'
+	 *   ]
+	 * ]
+	 *
+	 * @param array $i18n_partial A tree that follows the format of i18n-theme.json.
+	 * @param array $current_path Keeps track of the path as we walk down the given tree.
+	 *
+	 * @return array A linear array containing the paths to translate.
+	 */
+	private static function extract_paths_to_translate( $i18n_partial, $current_path = array() ) {
+		$result = array();
+		foreach ( $i18n_partial as $property => $partial_child ) {
+			if ( is_numeric( $property ) ) {
+				foreach ( $partial_child as $key => $context ) {
+					return array(
+						array(
+							'path'    => $current_path,
+							'key'     => $key,
+							'context' => $context,
+						),
+					);
+				}
+			}
+			$result = array_merge(
+				$result,
+				self::extract_paths_to_translate( $partial_child, array_merge( $current_path, array( $property ) ) )
+			);
+		}
+		return $result;
+	}
+
+	/**
+	 * Returns a data structure used in theme.json translation.
+	 *
+	 * @return array An array of theme.json fields that are translatable and the keys that are translatable
+	 */
+	public static function get_fields_to_translate() {
+		if ( null === self::$theme_json_i18n ) {
+			$file_structure        = self::read_json_file( __DIR__ . '/theme-i18n.json' );
+			self::$theme_json_i18n = self::extract_paths_to_translate( $file_structure );
+		}
+		return self::$theme_json_i18n;
+	}
+
+	/**
+	 * Translates a chunk of the loaded theme.json structure.
+	 *
+	 * @param array  $array_to_translate The chunk of theme.json to translate.
+	 * @param string $key                The key of the field that contains the string to translate.
+	 * @param string $context            The context to apply in the translation call.
+	 * @param string $domain             Text domain. Unique identifier for retrieving translated strings.
+	 *
+	 * @return array Returns the modified $theme_json chunk.
+	 */
+	private static function translate_theme_json_chunk( array $array_to_translate, $key, $context, $domain ) {
+		foreach ( $array_to_translate as $item_key => $item_to_translate ) {
+			if ( empty( $item_to_translate[ $key ] ) ) {
+				continue;
+			}
+
+			// phpcs:ignore WordPress.WP.I18n.LowLevelTranslationFunction,WordPress.WP.I18n.NonSingularStringLiteralText,WordPress.WP.I18n.NonSingularStringLiteralContext,WordPress.WP.I18n.NonSingularStringLiteralDomain
+			$array_to_translate[ $item_key ][ $key ] = translate_with_gettext_context( $array_to_translate[ $item_key ][ $key ], $context, $domain );
+		}
+
+		return $array_to_translate;
+	}
+
+	/**
+	 * Given a theme.json structure modifies it in place
+	 * to update certain values by its translated strings
+	 * according to the language set by the user.
+	 *
+	 * @param array  $theme_json The theme.json to translate.
+	 * @param string $domain    Optional. Text domain. Unique identifier for retrieving translated strings.
+	 *                          Default 'default'.
+	 *
+	 * @return array Returns the modified $theme_json_structure.
+	 */
+	private static function translate( $theme_json, $domain = 'default' ) {
+		$fields = self::get_fields_to_translate();
+		foreach ( $fields as $field ) {
+			$path    = $field['path'];
+			$key     = $field['key'];
+			$context = $field['context'];
+
+			/*
+			 * We need to process the paths that include '*' separately.
+			 * One example of such a path would be:
+			 * [ 'settings', 'blocks', '*', 'color', 'palette' ]
+			 */
+			$nodes_to_iterate = array_keys( $path, '*', true );
+			if ( ! empty( $nodes_to_iterate ) ) {
+				/*
+				 * At the moment, we only need to support one '*' in the path, so take it directly.
+				 * - base will be [ 'settings', 'blocks' ]
+				 * - data will be [ 'color', 'palette' ]
+				 */
+				$base_path = array_slice( $path, 0, $nodes_to_iterate[0] );
+				$data_path = array_slice( $path, $nodes_to_iterate[0] + 1 );
+				$base_tree = _wp_array_get( $theme_json, $base_path, array() );
+				foreach ( $base_tree as $node_name => $node_data ) {
+					$array_to_translate = _wp_array_get( $node_data, $data_path, null );
+					if ( is_null( $array_to_translate ) ) {
+						continue;
+					}
+
+					// Whole path will be [ 'settings', 'blocks', 'core/paragraph', 'color', 'palette' ].
+					$whole_path       = array_merge( $base_path, array( $node_name ), $data_path );
+					$translated_array = self::translate_theme_json_chunk( $array_to_translate, $key, $context, $domain );
+					_wp_array_set( $theme_json, $whole_path, $translated_array );
+				}
+			} else {
+				$array_to_translate = _wp_array_get( $theme_json, $path, null );
+				if ( is_null( $array_to_translate ) ) {
+					continue;
+				}
+
+				$translated_array = self::translate_theme_json_chunk( $array_to_translate, $key, $context, $domain );
+				_wp_array_set( $theme_json, $path, $translated_array );
+			}
+		}
+
+		return $theme_json;
+	}
+
+	/**
+	 * Return core's origin config.
+	 *
+	 * @return WP_Theme_JSON Entity that holds core data.
+	 */
+	public static function get_core_data() {
+		if ( null !== self::$core ) {
+			return self::$core;
+		}
+
+		$config     = self::read_json_file( __DIR__ . '/theme.json' );
+		$config     = self::translate( $config );
+		self::$core = new WP_Theme_JSON( $config );
+
+		return self::$core;
+	}
+
+	/**
+	 * Returns the theme's data.
+	 *
+	 * Data from theme.json can be augmented via the
+	 * $theme_support_data variable. This is useful, for example,
+	 * to backfill the gaps in theme.json that a theme has declared
+	 * via add_theme_supports.
+	 *
+	 * Note that if the same data is present in theme.json
+	 * and in $theme_support_data, the theme.json's is not overwritten.
+	 *
+	 * @param array $theme_support_data Theme support data in theme.json format.
+	 *
+	 * @return WP_Theme_JSON Entity that holds theme data.
+	 */
+	public static function get_theme_data( $theme_support_data = array() ) {
+		if ( null === self::$theme ) {
+			$theme_json_data = self::read_json_file( self::get_file_path_from_theme( 'theme.json' ) );
+			$theme_json_data = self::translate( $theme_json_data, wp_get_theme()->get( 'TextDomain' ) );
+			self::$theme     = new WP_Theme_JSON( $theme_json_data );
+		}
+
+		if ( empty( $theme_support_data ) ) {
+			return self::$theme;
+		}
+
+		/*
+		 * We want the presets and settings declared in theme.json
+		 * to override the ones declared via add_theme_support.
+		 */
+		$with_theme_supports = new WP_Theme_JSON( $theme_support_data );
+		$with_theme_supports->merge( self::$theme );
+
+		return $with_theme_supports;
+	}
+
+	/**
+	 * There are different sources of data for a site:
+	 * core and theme.
+	 *
+	 * While the getters {@link get_core_data},
+	 * {@link get_theme_data} return the raw data
+	 * from the respective origins, this method merges them
+	 * all together.
+	 *
+	 * If the same piece of data is declared in different origins (core and theme),
+	 * the last origin overrides the previous. For example,
+	 * if core disables custom colors but a theme enables them,
+	 * the theme config wins.
+	 *
+	 * @param array  $settings Existing block editor settings.
+	 *                         Empty array by default.
+	 *
+	 * @return WP_Theme_JSON
+	 */
+	public static function get_merged_data( $settings = array() ) {
+		$theme_support_data = WP_Theme_JSON::get_from_editor_settings( $settings );
+
+		$result = new WP_Theme_JSON();
+		$result->merge( self::get_core_data() );
+		$result->merge( self::get_theme_data( $theme_support_data ) );
+
+		return $result;
+	}
+
+	/**
+	 * Whether the current theme has a theme.json file.
+	 *
+	 * @return boolean
+	 */
+	public static function theme_has_support() {
+		if ( ! isset( self::$theme_has_support ) ) {
+			self::$theme_has_support = (bool) self::get_file_path_from_theme( 'theme.json' );
+		}
+
+		return self::$theme_has_support;
+	}
+
+	/**
+	 * Builds the path to the given file
+	 * and checks that it is readable.
+	 *
+	 * If it isn't, returns an empty string,
+	 * otherwise returns the whole file path.
+	 *
+	 * @param string $file_name Name of the file.
+	 * @return string The whole file path or empty if the file doesn't exist.
+	 */
+	private static function get_file_path_from_theme( $file_name ) {
+		// This used to be a locate_template call.
+		// However, that method proved problematic
+		// due to its use of constants (STYLESHEETPATH)
+		// that threw errors in some scenarios.
+		//
+		// When the theme.json merge algorithm properly supports
+		// child themes, this should also fallback
+		// to the template path, as locate_template did.
+		$located   = '';
+		$candidate = get_stylesheet_directory() . '/' . $file_name;
+		if ( is_readable( $candidate ) ) {
+			$located = $candidate;
+		}
+		return $located;
+	}
+
+	/**
+	 * Cleans the cached data so it can be recalculated.
+	 */
+	public static function clean_cached_data() {
+		self::$core                     = null;
+		self::$theme                    = null;
+		self::$theme_has_support        = null;
+		self::$theme_json_i18n          = null;
+	}
+
+}
+
+add_action( 'switch_theme', array( 'WP_Theme_JSON_Resolver', 'clean_cached_data' ) );
diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
new file mode 100644
index 000000000000..b78f7c9be41f
--- /dev/null
+++ b/wp-includes/class-wp-theme-json.php
@@ -0,0 +1,389 @@
+<?php
+/**
+ * Process of structures that adhere to the theme.json schema.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Class that encapsulates the processing of
+ * structures that adhere to the theme.json spec.
+ *
+ * @access private
+ */
+class WP_Theme_JSON {
+
+	/**
+	 * Container of data in theme.json format.
+	 *
+	 * @var array
+	 */
+	private $theme_json = null;
+
+	/**
+	 * Holds the allowed block names extracted from block.json.
+	 * Shared among all instances so we only process it once.
+	 *
+	 * @var array
+	 */
+	private static $allowed_block_names = null;
+
+	const ALLOWED_TOP_LEVEL_KEYS = array(
+		'version',
+		'settings',
+	);
+
+	const ALLOWED_SETTINGS = array(
+		'color'      => array(
+			'custom'         => null,
+			'customGradient' => null,
+			'duotone'        => null,
+			'gradients'      => null,
+			'link'           => null,
+			'palette'        => null,
+		),
+		'custom'     => null,
+		'layout'     => null,
+		'spacing'    => array(
+			'customMargin'  => null,
+			'customPadding' => null,
+			'units'         => null,
+		),
+		'typography' => array(
+			'customFontSize'   => null,
+			'customLineHeight' => null,
+			'dropCap'          => null,
+			'fontSizes'        => null,
+		),
+	);
+
+	const LATEST_SCHEMA = 1;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param array $theme_json A structure that follows the theme.json schema.
+	 */
+	public function __construct( $theme_json = array() ) {
+		if ( ! isset( $theme_json['version'] ) || self::LATEST_SCHEMA !== $theme_json['version'] ) {
+			$this->theme_json = array();
+			return;
+		}
+
+		$this->theme_json  = self::sanitize( $theme_json );
+	}
+
+	/**
+	 * Returns the allowed block names.
+	 *
+	 * @return array
+	 */
+	private static function get_allowed_block_names() {
+		if ( null !== self::$allowed_block_names ) {
+			return self::$allowed_block_names;
+		}
+
+		self::$allowed_block_names = array_keys( WP_Block_Type_Registry::get_instance()->get_all_registered() );
+
+		return self::$allowed_block_names;
+	}
+
+	/**
+	 * Sanitizes the input according to the schemas.
+	 *
+	 * @param array $input Structure to sanitize.
+	 *
+	 * @return array The sanitized output.
+	 */
+	private static function sanitize( $input ) {
+		$output = array();
+
+		if ( ! is_array( $input ) ) {
+			return $output;
+		}
+
+		$allowed_blocks = self::get_allowed_block_names();
+
+		$output = array_intersect_key( $input, array_flip( self::ALLOWED_TOP_LEVEL_KEYS ) );
+
+		// Build the schema.
+		$schema                 = array();
+		$schema_settings_blocks = array();
+		foreach ( $allowed_blocks as $block ) {
+			$schema_settings_blocks[ $block ] = self::ALLOWED_SETTINGS;
+		}
+		$schema['settings']           = self::ALLOWED_SETTINGS;
+		$schema['settings']['blocks'] = $schema_settings_blocks;
+
+		// Remove anything that's not present in the schema.
+		foreach ( array( 'settings' ) as $subtree ) {
+			if ( ! isset( $input[ $subtree ] ) ) {
+				continue;
+			}
+
+			if ( ! is_array( $input[ $subtree ] ) ) {
+				unset( $output[ $subtree ] );
+				continue;
+			}
+
+			$result = self::remove_keys_not_in_schema( $input[ $subtree ], $schema[ $subtree ] );
+
+			if ( empty( $result ) ) {
+				unset( $output[ $subtree ] );
+			} else {
+				$output[ $subtree ] = $result;
+			}
+		}
+
+		return $output;
+	}
+
+	/**
+	 * Given a tree, removes the keys that are not present in the schema.
+	 *
+	 * It is recursive and modifies the input in-place.
+	 *
+	 * @param array $tree Input to process.
+	 * @param array $schema Schema to adhere to.
+	 *
+	 * @return array Returns the modified $tree.
+	 */
+	private static function remove_keys_not_in_schema( $tree, $schema ) {
+		$tree = array_intersect_key( $tree, $schema );
+
+		foreach ( $schema as $key => $data ) {
+			if ( ! isset( $tree[ $key ] ) ) {
+				continue;
+			}
+
+			if ( is_array( $schema[ $key ] ) && is_array( $tree[ $key ] ) ) {
+				$tree[ $key ] = self::remove_keys_not_in_schema( $tree[ $key ], $schema[ $key ] );
+
+				if ( empty( $tree[ $key ] ) ) {
+					unset( $tree[ $key ] );
+				}
+			} elseif ( is_array( $schema[ $key ] ) && ! is_array( $tree[ $key ] ) ) {
+				unset( $tree[ $key ] );
+			}
+		}
+
+		return $tree;
+	}
+
+	/**
+	 * Returns the existing settings for each block.
+	 *
+	 * Example:
+	 *
+	 * {
+	 *   'root': {
+	 *     'color': {
+	 *       'custom': true
+	 *     }
+	 *   },
+	 *   'core/paragraph': {
+	 *     'spacing': {
+	 *       'customPadding': true
+	 *     }
+	 *   }
+	 * }
+	 *
+	 * @return array Settings per block.
+	 */
+	public function get_settings() {
+		if ( ! isset( $this->theme_json['settings'] ) ) {
+			return array();
+		} else {
+			return $this->theme_json['settings'];
+		}
+	}
+
+	/**
+	 * Builds metadata for the setting nodes, which returns in the form of:
+	 *
+	 * [
+	 *   [
+	 *     'path' => ['path', 'to', 'some', 'node' ]
+	 *   ],
+	 *   [
+	 *     'path' => [ 'path', 'to', 'other', 'node' ]
+	 *   ],
+	 * ]
+	 *
+	 * @param array $theme_json The tree to extract setting nodes from.
+	 *
+	 * @return array
+	 */
+	private static function get_setting_nodes( $theme_json ) {
+		$nodes = array();
+		if ( ! isset( $theme_json['settings'] ) ) {
+			return $nodes;
+		}
+
+		// Top-level.
+		$nodes[] = array(
+			'path' => array( 'settings' ),
+		);
+
+		// Calculate paths for blocks.
+		if ( ! isset( $theme_json['settings']['blocks'] ) ) {
+			return $nodes;
+		}
+
+		foreach ( $theme_json['settings']['blocks'] as $name => $node ) {
+			$nodes[] = array(
+				'path' => array( 'settings', 'blocks', $name ),
+			);
+		}
+
+		return $nodes;
+	}
+
+	/**
+	 * Merge new incoming data.
+	 *
+	 * @param WP_Theme_JSON $incoming Data to merge.
+	 */
+	public function merge( $incoming ) {
+		$incoming_data    = $incoming->get_raw_data();
+		$this->theme_json = array_replace_recursive( $this->theme_json, $incoming_data );
+
+		// The array_replace_recursive algorithm merges at the leaf level.
+		// For leaf values that are arrays it will use the numeric indexes for replacement.
+		// In those cases, what we want is to use the incoming value, if it exists.
+		//
+		// These are the cases that have array values at the leaf levels.
+		$properties   = array();
+		$properties[] = array( 'color', 'palette' );
+		$properties[] = array( 'color', 'gradients' );
+		$properties[] = array( 'custom' );
+		$properties[] = array( 'spacing', 'units' );
+		$properties[] = array( 'typography', 'fontSizes' );
+		$properties[] = array( 'typography', 'fontFamilies' );
+
+		$nodes = self::get_setting_nodes( $this->theme_json );
+		foreach ( $nodes as $metadata ) {
+			foreach ( $properties as $property_path ) {
+				$path = array_merge( $metadata['path'], $property_path );
+				$node = _wp_array_get( $incoming_data, $path, array() );
+				if ( ! empty( $node ) ) {
+					_wp_array_set( $this->theme_json, $path, $node );
+				}
+			}
+		}
+
+	}
+
+	/**
+	 * Returns the raw data.
+	 *
+	 * @return array Raw data.
+	 */
+	public function get_raw_data() {
+		return $this->theme_json;
+	}
+
+	/**
+	 *
+	 * Transforms the given editor settings according the
+	 * add_theme_support format to the theme.json format.
+	 *
+	 * @param array $settings Existing editor settings.
+	 *
+	 * @return array Config that adheres to the theme.json schema.
+	 */
+	public static function get_from_editor_settings( $settings ) {
+		$theme_settings = array(
+			'version'  => self::LATEST_SCHEMA,
+			'settings' => array(),
+		);
+
+		// Deprecated theme supports.
+		if ( isset( $settings['disableCustomColors'] ) ) {
+			if ( ! isset( $theme_settings['settings']['color'] ) ) {
+				$theme_settings['settings']['color'] = array();
+			}
+			$theme_settings['settings']['color']['custom'] = ! $settings['disableCustomColors'];
+		}
+
+		if ( isset( $settings['disableCustomGradients'] ) ) {
+			if ( ! isset( $theme_settings['settings']['color'] ) ) {
+				$theme_settings['settings']['color'] = array();
+			}
+			$theme_settings['settings']['color']['customGradient'] = ! $settings['disableCustomGradients'];
+		}
+
+		if ( isset( $settings['disableCustomFontSizes'] ) ) {
+			if ( ! isset( $theme_settings['settings']['typography'] ) ) {
+				$theme_settings['settings']['typography'] = array();
+			}
+			$theme_settings['settings']['typography']['customFontSize'] = ! $settings['disableCustomFontSizes'];
+		}
+
+		if ( isset( $settings['enableCustomLineHeight'] ) ) {
+			if ( ! isset( $theme_settings['settings']['typography'] ) ) {
+				$theme_settings['settings']['typography'] = array();
+			}
+			$theme_settings['settings']['typography']['customLineHeight'] = $settings['enableCustomLineHeight'];
+		}
+
+		if ( isset( $settings['enableCustomUnits'] ) ) {
+			if ( ! isset( $theme_settings['settings']['spacing'] ) ) {
+				$theme_settings['settings']['spacing'] = array();
+			}
+			$theme_settings['settings']['spacing']['units'] = ( true === $settings['enableCustomUnits'] ) ?
+				array( 'px', 'em', 'rem', 'vh', 'vw' ) :
+				$settings['enableCustomUnits'];
+		}
+
+		if ( isset( $settings['colors'] ) ) {
+			if ( ! isset( $theme_settings['settings']['color'] ) ) {
+				$theme_settings['settings']['color'] = array();
+			}
+			$theme_settings['settings']['color']['palette'] = $settings['colors'];
+		}
+
+		if ( isset( $settings['gradients'] ) ) {
+			if ( ! isset( $theme_settings['settings']['color'] ) ) {
+				$theme_settings['settings']['color'] = array();
+			}
+			$theme_settings['settings']['color']['gradients'] = $settings['gradients'];
+		}
+
+		if ( isset( $settings['fontSizes'] ) ) {
+			$font_sizes = $settings['fontSizes'];
+			// Back-compatibility for presets without units.
+			foreach ( $font_sizes as $key => $font_size ) {
+				if ( is_numeric( $font_size['size'] ) ) {
+					$font_sizes[ $key ]['size'] = $font_size['size'] . 'px';
+				}
+			}
+			if ( ! isset( $theme_settings['settings']['typography'] ) ) {
+				$theme_settings['settings']['typography'] = array();
+			}
+			$theme_settings['settings']['typography']['fontSizes'] = $font_sizes;
+		}
+
+		// This allows to make the plugin work with WordPress 5.7 beta
+		// as well as lower versions. The second check can be removed
+		// as soon as the minimum WordPress version for the plugin
+		// is bumped to 5.7.
+		if ( isset( $settings['enableCustomSpacing'] ) ) {
+			if ( ! isset( $theme_settings['settings']['spacing'] ) ) {
+				$theme_settings['settings']['spacing'] = array();
+			}
+			$theme_settings['settings']['spacing']['customPadding'] = $settings['enableCustomSpacing'];
+		}
+
+		// Things that didn't land in core yet, so didn't have a setting assigned.
+		if ( current( (array) get_theme_support( 'experimental-link-color' ) ) ) {
+			if ( ! isset( $theme_settings['settings']['color'] ) ) {
+				$theme_settings['settings']['color'] = array();
+			}
+			$theme_settings['settings']['color']['link'] = true;
+		}
+
+		return $theme_settings;
+	}
+
+}
diff --git a/wp-includes/theme-i18n.json b/wp-includes/theme-i18n.json
new file mode 100644
index 000000000000..a01a5aa566b4
--- /dev/null
+++ b/wp-includes/theme-i18n.json
@@ -0,0 +1,51 @@
+{
+	"settings": {
+		"typography": {
+				"fontSizes": [
+					{
+						"name": "Font size name"
+					}
+				]
+		},
+		"color": {
+				"palette": [
+					{
+						"name": "Color name"
+					}
+				],
+				"gradients": [
+					{
+						"name": "Gradient name"
+					}
+				],
+				"duotone": [
+					{
+						"name": "Duotone name"
+					}
+				]
+		},
+		"blocks": {
+			"*": {
+				"typography": {
+					"fontSizes": [
+						{
+							"name": "Font size name"
+						}
+					]
+				},
+				"color": {
+					"palette": [
+						{
+							"name": "Color name"
+						}
+					],
+					"gradients": [
+						{
+							"name": "Gradient name"
+						}
+					]
+				}
+			}
+		}
+	}
+}
diff --git a/wp-includes/theme.json b/wp-includes/theme.json
new file mode 100644
index 000000000000..eafaf0d69b37
--- /dev/null
+++ b/wp-includes/theme.json
@@ -0,0 +1,213 @@
+{
+	"version": 1,
+	"settings": {
+		"color": {
+			"custom": true,
+			"customGradient": true,
+			"duotone": [
+				{
+					"name":  "Dark grayscale" ,
+					"colors": [ "#000000", "#7f7f7f" ],
+					"slug": "dark-grayscale"
+				},
+				{
+					"name":  "Grayscale" ,
+					"colors": [ "#000000", "#ffffff" ],
+					"slug": "grayscale"
+				},
+				{
+					"name":  "Purple and yellow" ,
+					"colors": [ "#8c00b7", "#fcff41" ],
+					"slug": "purple-yellow"
+				},
+				{
+					"name":  "Blue and red" ,
+					"colors": [ "#000097", "#ff4747" ],
+					"slug": "blue-red"
+				},
+				{
+					"name":  "Midnight" ,
+					"colors": [ "#000000", "#00a5ff" ],
+					"slug": "midnight"
+				},
+				{
+					"name":  "Magenta and yellow" ,
+					"colors": [ "#c7005a", "#fff278" ],
+					"slug": "magenta-yellow"
+				},
+				{
+					"name":  "Purple and green" ,
+					"colors": [ "#a60072", "#67ff66" ],
+					"slug": "purple-green"
+				},
+				{
+					"name":  "Blue and orange" ,
+					"colors": [ "#1900d8", "#ffa96b" ],
+					"slug": "blue-orange"
+				}
+			],
+			"gradients": [
+				{
+					"name": "Vivid cyan blue to vivid purple",
+					"gradient": "linear-gradient(135deg,rgba(6,147,227,1) 0%,rgb(155,81,224) 100%)",
+					"slug": "vivid-cyan-blue-to-vivid-purple"
+				},
+				{
+					"name": "Light green cyan to vivid green cyan",
+					"gradient": "linear-gradient(135deg,rgb(122,220,180) 0%,rgb(0,208,130) 100%)",
+					"slug": "light-green-cyan-to-vivid-green-cyan"
+				},
+				{
+					"name": "Luminous vivid amber to luminous vivid orange",
+					"gradient": "linear-gradient(135deg,rgba(252,185,0,1) 0%,rgba(255,105,0,1) 100%)",
+					"slug": "luminous-vivid-amber-to-luminous-vivid-orange"
+				},
+				{
+					"name": "Luminous vivid orange to vivid red",
+					"gradient": "linear-gradient(135deg,rgba(255,105,0,1) 0%,rgb(207,46,46) 100%)",
+					"slug": "luminous-vivid-orange-to-vivid-red"
+				},
+				{
+					"name": "Very light gray to cyan bluish gray",
+					"gradient": "linear-gradient(135deg,rgb(238,238,238) 0%,rgb(169,184,195) 100%)",
+					"slug": "very-light-gray-to-cyan-bluish-gray"
+				},
+				{
+					"name": "Cool to warm spectrum",
+					"gradient": "linear-gradient(135deg,rgb(74,234,220) 0%,rgb(151,120,209) 20%,rgb(207,42,186) 40%,rgb(238,44,130) 60%,rgb(251,105,98) 80%,rgb(254,248,76) 100%)",
+					"slug": "cool-to-warm-spectrum"
+				},
+				{
+					"name": "Blush light purple",
+					"gradient": "linear-gradient(135deg,rgb(255,206,236) 0%,rgb(152,150,240) 100%)",
+					"slug": "blush-light-purple"
+				},
+				{
+					"name": "Blush bordeaux",
+					"gradient": "linear-gradient(135deg,rgb(254,205,165) 0%,rgb(254,45,45) 50%,rgb(107,0,62) 100%)",
+					"slug": "blush-bordeaux"
+				},
+				{
+					"name": "Luminous dusk",
+					"gradient": "linear-gradient(135deg,rgb(255,203,112) 0%,rgb(199,81,192) 50%,rgb(65,88,208) 100%)",
+					"slug": "luminous-dusk"
+				},
+				{
+					"name": "Pale ocean",
+					"gradient": "linear-gradient(135deg,rgb(255,245,203) 0%,rgb(182,227,212) 50%,rgb(51,167,181) 100%)",
+					"slug": "pale-ocean"
+				},
+				{
+					"name": "Electric grass",
+					"gradient": "linear-gradient(135deg,rgb(202,248,128) 0%,rgb(113,206,126) 100%)",
+					"slug": "electric-grass"
+				},
+				{
+					"name": "Midnight",
+					"gradient": "linear-gradient(135deg,rgb(2,3,129) 0%,rgb(40,116,252) 100%)",
+					"slug": "midnight"
+				}
+			],
+			"link": false,
+			"palette": [
+				{
+					"name": "Black",
+					"slug": "black",
+					"color": "#000000"
+				},
+				{
+					"name": "Cyan bluish gray",
+					"slug": "cyan-bluish-gray",
+					"color": "#abb8c3"
+				},
+				{
+					"name": "White",
+					"slug": "white",
+					"color": "#ffffff"
+				},
+				{
+					"name": "Pale pink",
+					"slug": "pale-pink",
+					"color": "#f78da7"
+				},
+				{
+					"name": "Vivid red",
+					"slug": "vivid-red",
+					"color": "#cf2e2e"
+				},
+				{
+					"name": "Luminous vivid orange",
+					"slug": "luminous-vivid-orange",
+					"color": "#ff6900"
+				},
+				{
+					"name": "Luminous vivid amber",
+					"slug": "luminous-vivid-amber",
+					"color": "#fcb900"
+				},
+				{
+					"name": "Light green cyan",
+					"slug": "light-green-cyan",
+					"color": "#7bdcb5"
+				},
+				{
+					"name": "Vivid green cyan",
+					"slug": "vivid-green-cyan",
+					"color": "#00d084"
+				},
+				{
+					"name": "Pale cyan blue",
+					"slug": "pale-cyan-blue",
+					"color": "#8ed1fc"
+				},
+				{
+					"name": "Vivid cyan blue",
+					"slug": "vivid-cyan-blue",
+					"color": "#0693e3"
+				},
+				{
+					"name": "Vivid purple",
+					"slug": "vivid-purple",
+					"color": "#9b51e0"
+				}
+			]
+		},
+		"spacing": {
+			"customMargin": false,
+			"customPadding": false,
+			"units": [ "px", "em", "rem", "vh", "vw" ]
+		},
+		"typography": {
+			"customFontSize": true,
+			"customLineHeight": false,
+			"dropCap": true,
+			"fontSizes": [
+				{
+					"name": "Small",
+					"slug": "small",
+					"size": "13px"
+				},
+				{
+					"name": "Normal",
+					"slug": "normal",
+					"size": "16px"
+				},
+				{
+					"name": "Medium",
+					"slug": "medium",
+					"size": "20px"
+				},
+				{
+					"name": "Large",
+					"slug": "large",
+					"size": "36px"
+				},
+				{
+					"name": "Huge",
+					"slug": "huge",
+					"size": "42px"
+				}
+			]
+		}
+	}
+}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index d69f7755f5e7..4eb0e3750688 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.8-alpha-50958';
+$wp_version = '5.8-alpha-50959';
 
 /**
  * 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 79574e4b2fb0..45949fda9119 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -295,6 +295,8 @@
 require ABSPATH . WPINC . '/class-wp-block-parser.php';
 require ABSPATH . WPINC . '/blocks.php';
 require ABSPATH . WPINC . '/blocks/index.php';
+require ABSPATH . WPINC . '/class-wp-theme-json.php';
+require ABSPATH . WPINC . '/class-wp-theme-json-resolver.php';
 require ABSPATH . WPINC . '/block-editor.php';
 require ABSPATH . WPINC . '/block-patterns.php';
 require ABSPATH . WPINC . '/class-wp-block-supports.php';