diff --git a/core/modules/outside_in/js/outside_in.es6.js b/core/modules/outside_in/js/outside_in.es6.js
index eea9075cab..2424b4693e 100644
--- a/core/modules/outside_in/js/outside_in.es6.js
+++ b/core/modules/outside_in/js/outside_in.es6.js
@@ -3,7 +3,7 @@
  * Drupal's Settings Tray library.
  */
 
-(function ($, Drupal) {
+(function ($, Drupal, debounce) {
 
   'use strict';
 
@@ -77,7 +77,7 @@
    * Helper to toggle Edit mode.
    */
   function toggleEditMode() {
-    setEditModeState(!isInEditMode());
+    setEditModeState(!isInEditMode(), true);
   }
 
   /**
@@ -118,12 +118,30 @@
   }
 
   /**
+   * Display message describing edit mode.
+   *
+   * @todo Refactor to use Javascript Message API https://www.drupal.org/node/77245
+   */
+  function displayEditMessage() {
+    const editMsg = Drupal.t('You are now in edit mode.');
+    const msgDiv = document.createElement('div');
+    msgDiv.setAttribute('id', 'settings-tray-edit-message')
+    msgDiv.setAttribute('class', 'settings-tray-messages messages messages--status');
+    msgDiv.setAttribute('role', 'alert');
+    msgDiv.innerHTML = editMsg;
+    $(msgDiv).insertBefore('div.dialog-off-canvas__main-canvas').hide().fadeIn('slow');
+    Drupal.announce(editMsg);
+    $(msgDiv).on('click.outsidein', e => $(e.target).remove());
+  }
+
+
+  /**
    *  Helper to switch edit mode state.
    *
    * @param {boolean} editMode
    *  True enable edit mode, false disable edit mode.
    */
-  function setEditModeState(editMode) {
+  function setEditModeState(editMode , displayMessage = false) {
     if (!document.querySelector('[data-off-canvas-main-canvas]')) {
       throw new Error('data-off-canvas-main-canvas is missing from outside-in-page-wrapper.html.twig');
     }
@@ -135,6 +153,11 @@
       $editButton.text(Drupal.t('Editing'));
       closeToolbarTrays();
 
+      if (displayMessage) {
+        const displayFunction = debounce(displayEditMessage, 300, true);
+        displayFunction();
+      }
+
       $editables = $('[data-drupal-outsidein="editable"]').once('outsidein');
       if ($editables.length) {
         // Use event capture to prevent clicks on links.
@@ -179,6 +202,8 @@
       $editButton.text(Drupal.t('Edit'));
       closeOffCanvas();
       disableQuickEdit();
+      // Remove edit mode message.
+      $('#settings-tray-edit-message').remove();
     }
     getItemsToToggle().toggleClass('js-outside-in-edit-mode', editMode);
     $('.edit-mode-inactive').toggleClass('visually-hidden', editMode);
@@ -262,4 +287,4 @@
     }
   });
 
-})(jQuery, Drupal);
+})(jQuery, Drupal, Drupal.debounce);
diff --git a/core/modules/outside_in/js/outside_in.js b/core/modules/outside_in/js/outside_in.js
index 83416c26e6..493ed657ac 100644
--- a/core/modules/outside_in/js/outside_in.js
+++ b/core/modules/outside_in/js/outside_in.js
@@ -5,7 +5,7 @@
 * @preserve
 **/
 
-(function ($, Drupal) {
+(function ($, Drupal, debounce) {
 
   'use strict';
 
@@ -43,7 +43,7 @@
   }
 
   function toggleEditMode() {
-    setEditModeState(!isInEditMode());
+    setEditModeState(!isInEditMode(), true);
   }
 
   function preventClick(event) {
@@ -65,7 +65,23 @@
     $('.ui-dialog-off-canvas .ui-dialog-titlebar-close').trigger('click');
   }
 
+  function displayEditMessage() {
+    var editMsg = Drupal.t('You are now in edit mode.');
+    var msgDiv = document.createElement('div');
+    msgDiv.setAttribute('id', 'settings-tray-edit-message');
+    msgDiv.setAttribute('class', 'settings-tray-messages messages messages--status');
+    msgDiv.setAttribute('role', 'alert');
+    msgDiv.innerHTML = editMsg;
+    $(msgDiv).insertBefore('div.dialog-off-canvas__main-canvas').hide().fadeIn('slow');
+    Drupal.announce(editMsg);
+    $(msgDiv).on('click.outsidein', function (e) {
+      return $(e.target).remove();
+    });
+  }
+
   function setEditModeState(editMode) {
+    var displayMessage = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : false;
+
     if (!document.querySelector('[data-off-canvas-main-canvas]')) {
       throw new Error('data-off-canvas-main-canvas is missing from outside-in-page-wrapper.html.twig');
     }
@@ -77,6 +93,11 @@
       $editButton.text(Drupal.t('Editing'));
       closeToolbarTrays();
 
+      if (displayMessage) {
+        var displayFunction = debounce(displayEditMessage, 300, true);
+        displayFunction();
+      }
+
       $editables = $('[data-drupal-outsidein="editable"]').once('outsidein');
       if ($editables.length) {
         document.querySelector('[data-off-canvas-main-canvas]').addEventListener('click', preventClick, true);
@@ -110,6 +131,8 @@
         $editButton.text(Drupal.t('Edit'));
         closeOffCanvas();
         disableQuickEdit();
+
+        $('#settings-tray-edit-message').remove();
       }
     getItemsToToggle().toggleClass('js-outside-in-edit-mode', editMode);
     $('.edit-mode-inactive').toggleClass('visually-hidden', editMode);
@@ -170,4 +193,4 @@
       }
     }
   });
-})(jQuery, Drupal);
\ No newline at end of file
+})(jQuery, Drupal, Drupal.debounce);
\ No newline at end of file
diff --git a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
index a5eacc5c53..107a055283 100644
--- a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
+++ b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
@@ -351,6 +351,7 @@ protected function assertEditModeEnabled() {
     $web_assert->elementContains('css', static::TOOLBAR_EDIT_LINK_SELECTOR, 'Editing');
     // The main canvas element should have the "js-outside-in-edit-mode" class.
     $web_assert->elementExists('css', '.dialog-off-canvas__main-canvas.js-outside-in-edit-mode');
+    $web_assert->elementTextContains('css', '#settings-tray-edit-message', 'You are now in edit mode');
   }
 
   /**
@@ -367,6 +368,7 @@ protected function assertEditModeDisabled() {
     // The main canvas element should NOT have the "js-outside-in-edit-mode"
     // class.
     $web_assert->elementNotExists('css', '.dialog-off-canvas__main-canvas.js-outside-in-edit-mode');
+    $web_assert->elementNotExists('css', '#settings-tray-edit-message');
   }
 
   /**