diff --git a/core/lib/Drupal/Core/Field/WidgetBase.php b/core/lib/Drupal/Core/Field/WidgetBase.php
index 24b1de5fa0..bafdb7708c 100644
--- a/core/lib/Drupal/Core/Field/WidgetBase.php
+++ b/core/lib/Drupal/Core/Field/WidgetBase.php
@@ -104,6 +104,19 @@ public function form(FieldItemListInterface $items, array &$form, FormStateInter
       $elements = $this->formMultipleElements($items, $form, $form_state);
     }
 
+    // Allow modules to alter the field multi-value widget form element.
+    // This hook can also be used for single-value fields.
+    $context = [
+      'form' => $form,
+      'widget' => $this,
+      'items' => $items,
+      'default' => $this->isDefaultValueWidget($form_state),
+    ];
+    \Drupal::moduleHandler()->alter([
+      'field_widget_multivalue_form',
+      'field_widget_multivalue_' . $this->getPluginId() . '_form',
+    ], $elements, $form_state, $context);
+
     // Populate the 'array_parents' information in $form_state->get('field')
     // after the form is built, so that we catch changes in the form structure
     // performed in alter() hooks.
@@ -241,19 +254,6 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
           ],
         ];
       }
-
-      // Allow modules to alter the field multi-value widget form element.
-      // This hook can also be used for single-value fields.
-      $context = [
-        'form' => $form,
-        'widget' => $this,
-        'items' => $items,
-        'default' => $this->isDefaultValueWidget($form_state),
-      ];
-      \Drupal::moduleHandler()->alter([
-        'field_widget_multivalue_form',
-        'field_widget_multivalue_' . $this->getPluginId() . '_form',
-      ], $elements, $form_state, $context);
     }
 
     return $elements;
diff --git a/core/modules/media/media.module b/core/modules/media/media.module
index 296945973a..cd8c842726 100644
--- a/core/modules/media/media.module
+++ b/core/modules/media/media.module
@@ -9,8 +9,10 @@
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Element\RenderElement;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Template\Attribute;
 use Drupal\Core\Url;
 use Drupal\field\FieldConfigInterface;
 
@@ -66,6 +68,10 @@ function media_theme() {
     'media' => [
       'render element' => 'elements',
     ],
+    'media_reference_help' => [
+      'render element' => 'element',
+      'base hook' => 'field_multiple_value_form',
+    ],
   ];
 }
 
@@ -172,3 +178,123 @@ function media_form_field_ui_field_storage_add_form_alter(&$form, FormStateInter
   $form['add']['new_storage_type']['#weight'] = 0;
   $form['add']['description_wrapper']['#weight'] = 1;
 }
+
+/**
+ * Implements hook_field_widget_multivalue_form_alter().
+ */
+function media_field_widget_multivalue_form_alter(array &$elements, FormStateInterface $form_state, array $context) {
+  // Only act on entity reference fields that reference media.
+  $field_type = $context['items']->getFieldDefinition()->getType();
+  $target_type = $context['items']->getFieldDefinition()->getFieldStorageDefinition()->getSetting('target_type');
+  if ($field_type !== 'entity_reference' ||  $target_type !== 'media') {
+    return;
+  }
+
+  // Autocomplete widgets need different help text than options widgets.
+  $widget_plugin_id = $context['widget']->getPluginId();
+  if (in_array($widget_plugin_id, array('entity_reference_autocomplete', 'entity_reference_autocomplete_tags'))) {
+    $is_autocomplete = TRUE;
+  }
+  else {
+    // @todo We can't yet properly alter non-autocomplete fields. Resolve this
+    //   in https://www.drupal.org/node/2943020 and remove this condition.
+    return;
+  }
+  $elements['#media_help'] = [];
+
+  // Retrieve the media bundle list and add information for the user based on
+  // which bundles are available to be created or referenced.
+  $settings = $context['items']->getFieldDefinition()->getSetting('handler_settings');
+  $allowed_bundles = $settings['target_bundles'];
+  $access_handler = \Drupal::entityTypeManager()->getAccessControlHandler('media');
+  $all_bundles = \Drupal::service('entity_type.bundle.info')->getBundleInfo('media');
+  $bundle_labels = [];
+  $create_bundles = [];
+  foreach ($allowed_bundles as $bundle) {
+    $bundle_labels[] = $all_bundles[$bundle]['label'];
+    if ($access_handler->createAccess($bundle)) {
+      $create_bundles[] = $bundle;
+      if (count($create_bundles) > 1) {
+        // If the user has access to create more than 1 bundle then the
+        // individual media type form can not be used.
+        break;
+      }
+    }
+  }
+
+  // Add a section about how to create media if the user has access to do so.
+  if (!empty($create_bundles)) {
+    if (count($create_bundles) === 1) {
+      $add_url =  Url::fromRoute('entity.media.add_form', ['media_type' => $create_bundles[0]])->toString();
+    }
+    elseif (count($create_bundles) > 1) {
+      $add_url = Url::fromRoute('entity.media.add_page')->toString();
+    }
+    $elements['#media_help']['#media_add_help'] = t('Create your media on the <a href=":add_page" target="_blank">media add page</a> (opens a new window), then add it by name to the field below.', [':add_page' => $add_url]);
+  }
+
+  $elements['#theme'] = 'media_reference_help';
+  // @todo template_preprocess_field_multiple_value_form() assumes this key
+  //   exists, but it does not exist in the case of a single widget that
+  //   accepts multiple values. This is for some reason necessary to use
+  //   our template for the entity_autocomplete_tags widget.
+  //   Research and resolve this in https://www.drupal.org/node/2943020.
+  if (empty($elements['#cardinality_multiple'])) {
+    $elements['#cardinality_multiple'] = NULL;
+  }
+
+  // Use the title set on the element if it exists, otherwise fall back to the
+  // field label.
+  $elements['#media_help']['#original_label'] = isset($elements['#title']) ? $elements['#title'] : $context['items']->getFieldDefinition()->getLabel();
+
+  // Customize the label for the field widget.
+  // @todo Research a better approach https://www.drupal.org/node/2943024.
+  $use_existing_label = t('Use existing media');
+  if (!empty($elements[0]['target_id']['#title'])) {
+    $elements[0]['target_id']['#title'] = $use_existing_label;
+  }
+  if (!empty($elements['#title'])) {
+    $elements['#title'] = $use_existing_label;
+  }
+  if (!empty($elements['target_id']['#title'])) {
+    $elements['target_id']['#title'] = $use_existing_label;
+  }
+
+  // This help text is only relevant for autocomplete widgets. When the user
+  // is presented with options, they don't need to type anything or know what
+  // types of media are allowed.
+  if ($is_autocomplete) {
+    $elements['#media_help']['#media_list_help'] = t('Type part of the media name.');
+
+    $overview_url = Url::fromRoute('entity.media.collection');
+    if ($overview_url->access()) {
+      $elements['#media_help']['#media_list_link'] = t('See the <a href=":list_url" target="_blank">media list</a> (opens a new window) to help locate media.', [':list_url' => $overview_url->toString()]);
+    }
+    $elements['#media_help']['#allowed_types_help'] = t('Allowed media types: %types', ['%types' => implode(", ", $bundle_labels)]);
+  }
+}
+
+/**
+ * Implements hook_preprocess_HOOK() for media reference widgets.
+ */
+function media_preprocess_media_reference_help(&$variables) {
+  // Most of these attribute checks are copied from
+  // template_preprocess_fieldset(). Our template extends
+  // field-multiple-value-form.html.twig to provide our help text, but also
+  // groups the information within a semantic fieldset with a legend. So, we
+  // incorporate parity for both.
+  $element = $variables['element'];
+  Element::setAttributes($element, ['id']);
+  RenderElement::setAttributes($element);
+  $variables['attributes'] = isset($element['#attributes']) ? $element['#attributes'] : [];
+  $variables['legend_attributes'] = new Attribute();
+  $variables['header_attributes'] = new Attribute();
+  $variables['description']['attributes'] = new Attribute();
+  $variables['legend_span_attributes'] = new Attribute();
+
+  if (!empty($element['#media_help'])) {
+    foreach ($element['#media_help'] as $key => $text) {
+      $variables[substr($key, 1)] = $text;
+    }
+  }
+}
diff --git a/core/modules/media/templates/media-reference-help.html.twig b/core/modules/media/templates/media-reference-help.html.twig
new file mode 100644
index 0000000000..9243c5d4fd
--- /dev/null
+++ b/core/modules/media/templates/media-reference-help.html.twig
@@ -0,0 +1,66 @@
+{#
+/**
+ * @file
+ * Theme override for media reference fields.
+ *
+ * @see template_preprocess_field_multiple_value_form()
+ * @see core/themes/classy/templates/form/fieldset.html.twig
+ */
+#}
+{%
+  set classes = [
+    'js-form-item',
+    'form-item',
+    'js-form-wrapper',
+    'form-wrapper',
+  ]
+%}
+<fieldset{{ attributes.addClass(classes) }}>
+  {%
+    set legend_span_classes = [
+      'fieldset-legend',
+      required ? 'js-form-required',
+      required ? 'form-required',
+    ]
+  %}
+  {#  Always wrap fieldset legends in a <span> for CSS positioning. #}
+  <legend{{ legend_attributes }}>
+    <span{{ legend_span_attributes.addClass(legend_span_classes) }}>{{ original_label }}</span>
+  </legend>
+
+  <div class="js-form-item form-item">
+    {% if media_add_help %}
+      <h4{{ header_attributes.addClass('label') }}>
+        {% trans %}
+          Create new media
+        {% endtrans %}
+      </h4><br />
+      <div class="description">
+        {{ media_add_help }}
+      </div>
+    {% endif %}
+
+    {% if multiple %}
+      {{ table }}
+    {% else %}
+      {% for element in elements %}
+        {{ element }}
+      {% endfor %}
+    {% endif %}
+
+    <div{{ description.attributes.addClass('description') }}>
+      {% if multiple and description.content %}
+        <ul>
+          <li>{{ media_list_help }} {{ media_list_link }} {{ allowed_types_help }}</li>
+          <li>{{ description.content }}</li>
+        </ul>
+      {% else %}
+        {{ media_list_help }} {{ media_list_link }} {{ allowed_types_help }}
+      {% endif %}
+      {% if multiple and button %}
+        <div class="clearfix">{{ button }}</div>
+      {% endif %}
+    </div>
+
+  </div>
+</fieldset>
diff --git a/core/modules/media/tests/src/Functional/MediaFunctionalTestTrait.php b/core/modules/media/tests/src/Functional/MediaFunctionalTestTrait.php
index 224bb426e3..379ba74717 100644
--- a/core/modules/media/tests/src/Functional/MediaFunctionalTestTrait.php
+++ b/core/modules/media/tests/src/Functional/MediaFunctionalTestTrait.php
@@ -14,6 +14,7 @@
    */
   protected static $adminUserPermissions = [
     // Media module permissions.
+    'access media overview',
     'administer media',
     'administer media fields',
     'administer media form display',
diff --git a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
index 8d876b7b0d..a6711f1dd8 100644
--- a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
+++ b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
@@ -2,7 +2,12 @@
 
 namespace Drupal\Tests\media\Functional;
 
+use Behat\Mink\Element\NodeElement;
 use Drupal\media\Entity\Media;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\Url;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
 
 /**
  * Ensures that media UI works correctly.
@@ -192,6 +197,316 @@ public function testRenderedEntityReferencedMedia() {
     $assert_session->fieldValueEquals('fields[field_foo_field][type]', 'entity_reference_entity_view');
   }
 
+  /**
+   * Data provider for testMediaReferenceWidget().
+   *
+   * @return array[]
+   *   Test data. See testMediaReferenceWidget() for the child array structure.
+   */
+  public function providerTestMediaReferenceWidget() {
+    return [
+      // Single-value fields with a single media type and the default widget:
+      // - The user can create and list the media.
+      'single_value:single_type:create_list' => [1, [TRUE], TRUE],
+      // - The user can list but not create the media.
+      'single_value:single_type:list' => [1, [FALSE], TRUE],
+      // - The user can create but not list the media.
+      'single_value:single_type:create' => [1, [TRUE], FALSE],
+      // - The user can neither create nor list the media.
+      'single_value:single_type' => [1, [FALSE], FALSE],
+
+      // Single-value fields with the tags-style widget:
+      // - The user can create and list the media.
+      'single_value:single_type:create_list:tags' => [1, [TRUE], TRUE, 'entity_reference_autocomplete_tags'],
+      // - The user can list but not create the media.
+      'single_value:single_type:list:tags' => [1, [FALSE], TRUE, 'entity_reference_autocomplete_tags'],
+      // - The user can create but not list the media.
+      'single_value:single_type:create:tags' => [1, [TRUE], FALSE, 'entity_reference_autocomplete_tags'],
+      // - The user can neither create nor list the media.
+      'single_value:single_type:tags' => [1, [FALSE], FALSE, 'entity_reference_autocomplete_tags'],
+
+      // Single-value fields with two media types:
+      // - The user can create both types.
+      'single_value:two_type:create2_list' => [1, [TRUE, TRUE], TRUE],
+      // - The user can create only one type.
+      'single_value:two_type:create1_list' => [1, [TRUE, FALSE], TRUE],
+      // - The user cannot create either type.
+      'single_value:two_type:list' => [1, [FALSE, FALSE], TRUE],
+
+      // Multiple-value field with a cardinality of 3, with media the user can
+      // create and list.
+      'multi_value:single_type:create_list' => [3, [TRUE], TRUE],
+      // The same, with the tags field.
+      'multi-value:single_type:create_list:tags' => [3, [TRUE], TRUE, 'entity_reference_autocomplete_tags'],
+
+      // Unlimited value field.
+      'unlimited_value:single_type:create_list' => [FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED, [TRUE], TRUE],
+      // Unlimited value field with the tags widget.
+      'unlimited_value:single_type:create_list' => [FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED, [TRUE], TRUE, 'entity_reference_autocomplete_tags'],
+    ];
+  }
+
+  /**
+   * Tests the default autocomplete widgets for media reference fields.
+   *
+   * @param int $cardinality
+   *   The field cardinality.
+   * @param bool[] $media_type_create_access
+   *   An array of booleans indicating whether to grant the test user create
+   *   access for each media type. A media type is created automatically for
+   *   each; for example, an array [TRUE, FALSE] would create two media types,
+   *   one that allows the user to create media and a second that does not.
+   * @param bool $list_access
+   *   Whether to grant the test user access to list media.
+   *
+   * @see media_field_widget_entity_reference_autocomplete_form_alter()
+   * @see media_field_widget_multiple_entity_reference_autocomplete_form_alter()
+   *
+   * @dataProvider providerTestMediaReferenceWidget
+   */
+  public function testMediaReferenceWidget($cardinality, array $media_type_create_access, $list_access, $widget_id = 'entity_reference_autocomplete') {
+    $assert_session = $this->assertSession();
+
+    // Create two content types.
+    $non_media_content_type = $this->createContentType();
+    $content_type = $this->createContentType();
+
+    // Create some media types.
+    $media_types = [];
+    $permissions = [];
+    $create_media_types = [];
+    foreach ($media_type_create_access as $id => $access) {
+      if ($access) {
+        $create_media_types[] = "media_type_$id";
+        $permissions[] = "create media_type_$id media";
+      }
+      $this->createMediaType(['bundle' => "media_type_$id"]);
+      $media_types["media_type_$id"] = "media_type_$id";
+    }
+
+    // Create a user that can create content of the type, with other
+    // permissions as given by the data provider.
+    $permissions[] = "create {$content_type->id()} content";
+    if ($list_access) {
+      $permissions[] = "access media overview";
+    }
+    $test_user = $this->drupalCreateUser($permissions);
+
+    // Create a non-media entity reference.
+    $non_media_storage = FieldStorageConfig::create([
+      'field_name' => 'field_not_a_media_field',
+      'entity_type' => 'node',
+      'type' => 'entity_reference',
+      'cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
+      'settings' => [
+        'target_type' => 'node',
+      ],
+    ]);
+    $non_media_storage->save();
+    $non_media_field = FieldConfig::create([
+      'label' => 'No media here!',
+      'field_storage' => $non_media_storage,
+      'entity_type' => 'node',
+      'bundle' => $non_media_content_type->id(),
+      'settings' => [
+        'handler' => 'default',
+        'handler_settings' => [
+          'target_bundles' => [
+            $non_media_content_type->id() => $non_media_content_type->id(),
+          ],
+        ],
+      ],
+    ]);
+    $non_media_field->save();
+    \Drupal::entityTypeManager()
+      ->getStorage('entity_form_display')
+      ->load('node.' . $non_media_content_type->id() . '.default')
+      ->setComponent('field_not_a_media_field', [
+        'type' => $widget_id,
+      ])
+      ->save();
+
+    // Create a media field.
+    $storage = FieldStorageConfig::create([
+      'field_name' => "field_media_reference",
+      'entity_type' => 'node',
+      'type' => 'entity_reference',
+      'cardinality' => $cardinality,
+      'settings' => [
+        'target_type' => 'media',
+      ],
+    ]);
+    $storage->save();
+    $field = FieldConfig::create([
+      'label' => "Media (cardinality $cardinality)",
+      'field_storage' => $storage,
+      'entity_type' => 'node',
+      'bundle' => $content_type->id(),
+      'settings' => [
+        'handler' => 'default',
+        'handler_settings' => [
+          'target_bundles' => $media_types,
+        ],
+      ],
+    ]);
+    $field->save();
+    \Drupal::entityTypeManager()
+      ->getStorage('entity_form_display')
+      ->load('node.' . $content_type->id() . '.default')
+      ->setComponent('field_media_reference', [
+        'type' => $widget_id,
+      ])
+      ->save();
+
+    // Some of the expected texts.
+    $create_help = 'Create your media on the media add page (opens a new window), then add it by name to the field below.';
+    $list_text = 'See the media list (opens a new window) to help locate media.';
+    $use_help = 'Type part of the media name.';
+    $create_header = "Create new media";
+    $use_header = "Use existing media";
+
+    // First check that none of the help texts are on the non-media content.
+    $this->drupalGet("/node/add/{$non_media_content_type->id()}");
+    $this->assertNoHelpTexts([
+      $create_header,
+      $create_help,
+      $use_header,
+      $use_help,
+      $list_text,
+      'Allowed media types:',
+    ]);
+
+    // Now, check that the widget displays the expected help text under the
+    // given conditions for the test user.
+    $this->drupalLogin($test_user);
+    $this->drupalGet("/node/add/{$content_type->id()}");
+
+    // Specific expected help texts for the media field.
+    $create_header = "Create new media";
+    $use_header = "Use existing media";
+    $type_list = 'Allowed media types: ' . implode(", ", array_keys($media_types));
+
+    $fieldset_selector = '#edit-field-media-reference-wrapper fieldset';
+    $fieldset = $assert_session->elementExists('css', $fieldset_selector);
+
+    $this->assertSame($field->getLabel(), $assert_session->elementExists('css', 'legend', $fieldset)->getText());
+
+    // Assert text that should be displayed regardless of other access.
+    $this->assertHelpTexts([$use_header, $use_help, $type_list], $fieldset_selector);
+
+    // The entire section for creating new media should only be displayed if
+    // the user can create at least one media of the type.
+    if ($create_media_types) {
+      if (count($create_media_types) === 1) {
+        $url = Url::fromRoute('entity.media.add_form')->setRouteParameter('media_type', $create_media_types[0]);
+      }
+      else {
+        $url = Url::fromRoute('entity.media.add_page');
+      }
+      $this->assertHelpTexts([$create_header, $create_help], $fieldset_selector);
+      $this->assertHelpLink(
+        $fieldset,
+        'media add page',
+        [
+          'target' => '_blank',
+          'href' => $url->toString(),
+        ]
+      );
+    }
+    else {
+      $this->assertNoHelpTexts([$create_header, $create_help]);
+      $this->assertNoHelpLink($fieldset, 'media add page');
+    }
+
+    if ($list_access) {
+      $this->assertHelpTexts([$list_text], $fieldset_selector);
+      $this->assertHelpLink(
+        $fieldset,
+        'media list',
+        [
+          'target' => '_blank',
+          'href' => Url::fromRoute('entity.media.collection')->toString(),
+        ]
+      );
+    }
+    else {
+      $this->assertNoHelpTexts([$list_text]);
+      $this->assertNoHelpLink($fieldset, 'media list');
+    }
+  }
+
+  /**
+   * Asserts that the given texts are present exactly once.
+   *
+   * @param string[] $texts
+   *   A list of the help texts to check.
+   * @param string $selector
+   *   (optional) The selector to search.
+   */
+  public function assertHelpTexts(array $texts, $selector = '') {
+    $assert_session = $this->assertSession();
+    foreach ($texts as $text) {
+      // We only want to escape single quotes, so use str_replace() rather than
+      // addslashes().
+      $text = str_replace("'", "\'", $text);
+      if ($selector) {
+        $assert_session->elementsCount('css', $selector . ":contains('$text')", 1);
+      }
+      else {
+        $assert_session->pageTextContains($text);
+      }
+    }
+  }
+
+  /**
+   * Asserts that none of the given texts are present.
+   *
+   * @param string[] $texts
+   *   A list of the help texts to check.
+   */
+  public function assertNoHelpTexts(array $texts) {
+    $assert_session = $this->assertSession();
+    foreach ($texts as $text) {
+      $assert_session->pageTextNotContains($text);
+    }
+  }
+
+  /**
+   * Asserts whether a given link is present.
+   *
+   * @param \Behat\Mink\Element\NodeElement $element
+   *   The element to search.
+   * @param string $text
+   *   The link text.
+   * @param string[] attributes
+   *   An associative array of any expected attributes, keyed by the
+   *   attribute name.
+   */
+  protected function assertHelpLink(NodeElement $element, $text, array $attributes = []) {
+    // Find all the links inside the element.
+    $link = $element->findLink($text);
+
+    $this->assertNotEmpty($link);
+    foreach ($attributes as $attribute => $value) {
+      $this->assertEquals($link->getAttribute($attribute), $value);
+    }
+  }
+
+  /**
+   * Asserts that a given link is not present.
+   *
+   * @param \Behat\Mink\Element\NodeElement $element
+   *   The element to search.
+   * @param string $text
+   *   The link text.
+   */
+  protected function assertNoHelpLink(NodeElement $element, $text) {
+    $assert_session = $this->assertSession();
+    // Assert that the link and its text are not present anywhere on the page.
+    $assert_session->elementNotExists('named', ['link', $text], $element);
+    $assert_session->pageTextNotContains($text);
+  }
+
   /**
    * Test the media collection route.
    */
