diff --git a/src/js/_enqueues/wp/customize/controls.js b/src/js/_enqueues/wp/customize/controls.js
index 00ec7e2599..37a57fd859 100644
--- a/src/js/_enqueues/wp/customize/controls.js
+++ b/src/js/_enqueues/wp/customize/controls.js
@@ -8334,6 +8334,33 @@
 				history.replaceState( {}, document.title, urlParser.href );
 			}
 
+			/**
+			 * Displays a Site Editor notification when a block theme is activated.
+			 *
+			 * @since 4.9.0
+			 *
+			 * @param {string} [notification] - A notification to display.
+			 * @return {void}
+			 */
+			function addSiteEditorNotification( notification ) {
+				api.notifications.add( new api.Notification( 'site_editor_block_theme_notice', {
+					message: notification,
+					type: 'info',
+					dismissible: false,
+					render: function() {
+						var notification = api.Notification.prototype.render.call( this ),
+							button = notification.find( 'button.switch-to-editor' );
+
+						button.on( 'click', function( event ) {
+							event.preventDefault();
+							location.assign( button.data( 'action' ) );
+						} );
+
+						return notification;
+					}
+				} ) );
+			}
+
 			/**
 			 * Dismiss autosave.
 			 *
@@ -8408,6 +8435,10 @@
 			if ( api.settings.changeset.latestAutoDraftUuid || api.settings.changeset.hasAutosaveRevision ) {
 				addAutosaveRestoreNotification();
 			}
+			var shouldDisplayBlockThemeNotification = !! parseInt( $( '#customize-info' ).data( 'block-theme' ), 10 );
+			if (shouldDisplayBlockThemeNotification) {
+				addSiteEditorNotification( api.l10n.blockThemeNotification );
+			}
 		})();
 
 		// Check if preview url is valid and load the preview frame.
diff --git a/src/wp-admin/css/customize-controls.css b/src/wp-admin/css/customize-controls.css
index bdd28880c1..20596fa23c 100644
--- a/src/wp-admin/css/customize-controls.css
+++ b/src/wp-admin/css/customize-controls.css
@@ -1733,6 +1733,12 @@ p.customize-section-description {
 	font-weight: 400;
 }
 
+#customize-notifications-area .notification-message button.switch-to-editor {
+	display: block;
+	margin-top: 6px;
+	font-weight: 400;
+}
+
 #customize-theme-controls .control-panel-themes > .accordion-section-title:after {
 	display: none;
 }
diff --git a/src/wp-admin/customize.php b/src/wp-admin/customize.php
index aed0646336..0df5d81ae5 100644
--- a/src/wp-admin/customize.php
+++ b/src/wp-admin/customize.php
@@ -222,7 +222,7 @@ do_action( 'customize_controls_head' );
 				<ul></ul>
 			</div>
 			<div class="wp-full-overlay-sidebar-content" tabindex="-1">
-				<div id="customize-info" class="accordion-section customize-info">
+				<div id="customize-info" class="accordion-section customize-info" data-block-theme="<?php echo (int) wp_is_block_theme(); ?>">
 					<div class="accordion-section-title">
 						<span class="preview-notice">
 						<?php
@@ -235,7 +235,7 @@ do_action( 'customize_controls_head' );
 					<div class="customize-panel-description">
 						<p>
 							<?php
-							_e( 'The Customizer allows you to preview changes to your site before publishing them. You can navigate to different pages on your site within the preview. Edit shortcuts are shown for some editable elements.' );
+							_e( 'The Customizer allows you to preview changes to your site before publishing them. You can navigate to different pages on your site within the preview. Edit shortcuts are shown for some editable elements. The Customizer is intended for use with non-block themes.' );
 							?>
 						</p>
 						<p>
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 6b7ccea2f7..1469d42762 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -1154,6 +1154,7 @@ function wp_default_scripts( $scripts ) {
 	$scripts->add( 'customize-models', '/wp-includes/js/customize-models.js', array( 'underscore', 'backbone' ), false, 1 );
 	$scripts->add( 'customize-views', '/wp-includes/js/customize-views.js', array( 'jquery', 'underscore', 'imgareaselect', 'customize-models', 'media-editor', 'media-views' ), false, 1 );
 	$scripts->add( 'customize-controls', "/wp-admin/js/customize-controls$suffix.js", array( 'customize-base', 'wp-a11y', 'wp-util', 'jquery-ui-core' ), false, 1 );
+	$switch_to_site_editor_label = __( 'Use Site Editor' );
 	did_action( 'init' ) && $scripts->localize(
 		'customize-controls',
 		'_wpCustomizeControlsL10n',
@@ -1221,6 +1222,18 @@ function wp_default_scripts( $scripts ) {
 			'publishSettings'         => __( 'Publish Settings' ),
 			'invalidDate'             => __( 'Invalid date.' ),
 			'invalidValue'            => __( 'Invalid value.' ),
+			'blockThemeNotification'  => sprintf(
+				/* translators: 1. %s: URL to the localized version of https://wordpress.org/support/article/site-editor/, 2: HTML Button. */
+				__( 'Hurray! Your theme supports Full Site Editing with blocks. <a href="%1$s" target="_blank">Tell me more</a>. %2$s' ),
+				__( 'https://wordpress.org/support/article/site-editor/' ),
+				sprintf(
+					/* translators: 1: URL to the Site Editor admin screen, 2: Button label, 3: Button text. */
+					'<button type="button" data-action="%1$s" class="button switch-to-editor" aria-label="%2$s">%3$s</button>',
+					esc_url( admin_url( 'site-editor.php' ) ),
+					$switch_to_site_editor_label,
+					$switch_to_site_editor_label
+				)
+			),
 		)
 	);
 	$scripts->add( 'customize-selective-refresh', "/wp-includes/js/customize-selective-refresh$suffix.js", array( 'jquery', 'wp-util', 'customize-preview' ), false, 1 );