diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 96f810e..4f001ae 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -11,7 +11,6 @@
 use Drupal\Core\Language\Language;
 use Drupal\Core\ParamConverter\ParamNotConvertedException;
 use Drupal\Core\Routing\RequestHelper;
-use Drupal\Core\Template\Attribute;
 use Drupal\menu_link\Entity\MenuLink;
 use Drupal\menu_link\MenuLinkStorageController;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
@@ -1611,60 +1610,49 @@ function _menu_tree_data(&$links, $parents, $depth) {
 }
 
 /**
- * Implements template_preprocess_HOOK() for theme_menu_tree().
+ * Prepares variables for menu tree templates.
+ *
+ * Default template: menu-tree.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - tree: A render array for a menu tree.
  */
 function template_preprocess_menu_tree(&$variables) {
   $variables['tree'] = $variables['tree']['#children'];
 }
 
 /**
- * Returns HTML for a wrapper for a menu sub-tree.
+ * Prepares variables for menu link plus submenu templates.
  *
- * @param $variables
- *   An associative array containing:
- *   - tree: An HTML string containing the tree's items.
+ * Default template: menu-link.html.twig.
  *
- * @see template_preprocess_menu_tree()
- * @ingroup themeable
- */
-function theme_menu_tree($variables) {
-  return '<ul class="menu">' . $variables['tree'] . '</ul>';
-}
-
-/**
- * Returns HTML for a menu link and submenu.
- *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - element: Structured array data for a menu link.
- *
- * @ingroup themeable
  */
-function theme_menu_link(array $variables) {
+function template_preprocess_menu_link(&$variables) {
   $element = $variables['element'];
-  $sub_menu = '';
-
-  if ($element['#below']) {
-    $sub_menu = drupal_render($element['#below']);
-  }
   $element['#localized_options']['set_active_class'] = TRUE;
-  $output = l($element['#title'], $element['#href'], $element['#localized_options']);
-  return '<li' . new Attribute($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
+
+  $variables['sub_menu'] = $element['#below'];
+  $variables['link'] = l($element['#title'], $element['#href'], $element['#localized_options']);
+  $variables['attributes'] = $element['#attributes'];
 }
 
 /**
- * Returns HTML for a single local task link.
+ * Prepares variables for single local task link templates.
+ *
+ * Default template: menu-local-task.html.twig.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
  *   - element: A render element containing:
  *     - #link: A menu link array with 'title', 'href', and 'localized_options'
  *       keys.
  *     - #active: A boolean indicating whether the local task is active.
- *
- * @ingroup themeable
  */
-function theme_menu_local_task($variables) {
+function template_preprocess_menu_local_task(&$variables) {
   $link = $variables['element']['#link'];
   $link += array(
     'localized_options' => array(),
@@ -1674,6 +1662,7 @@ function theme_menu_local_task($variables) {
   if (!empty($variables['element']['#active'])) {
     // Add text to indicate active tab for non-visual users.
     $active = '<span class="visually-hidden">' . t('(active tab)') . '</span>';
+    $variables['attributes']['class'] = array('active');
 
     // If the link does not contain HTML already, String::checkPlain() it now.
     // After we set 'html'=TRUE the link will not be sanitized by l().
@@ -1693,21 +1682,21 @@ function theme_menu_local_task($variables) {
     $a_tag = \Drupal::l($link_text, $link['route_name'], $link['route_parameters'], $link['localized_options']);
   }
 
-  return '<li' . (!empty($variables['element']['#active']) ? ' class="active"' : '') . '>' . $a_tag . '</li>';
+  $variables['link'] = $a_tag;
 }
 
 /**
- * Returns HTML for a single local action link.
+ * Prepares variables for single local action link templates.
  *
- * @param $variables
+ * Default template: menu-local-action.html.twig.
+ *
+ * @param array $variables
  *   An associative array containing:
  *   - element: A render element containing:
  *     - #link: A menu link array with 'title', 'href', and 'localized_options'
  *       keys.
- *
- * @ingroup themeable
  */
-function theme_menu_local_action($variables) {
+function template_preprocess_menu_local_action(&$variables) {
   $link = $variables['element']['#link'];
   $link += array(
     'href' => '',
@@ -1718,19 +1707,15 @@ function theme_menu_local_action($variables) {
   $link['localized_options']['attributes']['class'][] = 'button-action';
   $link['localized_options']['set_active_class'] = TRUE;
 
-  $output = '<li>';
   // @todo Remove this check and the call to l() when all pages are converted to
   //   routes.
   // @todo Figure out how to support local actions without a href properly.
   if ($link['href'] === '' && !empty($link['route_name'])) {
-    $output .= Drupal::l($link['title'], $link['route_name'], $link['route_parameters'], $link['localized_options']);
+    $variables['link'] = Drupal::l($link['title'], $link['route_name'], $link['route_parameters'], $link['localized_options']);
   }
   else {
-    $output .= l($link['title'], $link['href'], $link['localized_options']);
+    $variables['link'] = l($link['title'], $link['href'], $link['localized_options']);
   }
-  $output .= "</li>";
-
-  return $output;
 }
 
 /**
@@ -2135,36 +2120,6 @@ function menu_local_tabs() {
 }
 
 /**
- * Returns HTML for primary and secondary local tasks.
- *
- * @param $variables
- *   An associative array containing:
- *     - primary: (optional) An array of local tasks (tabs).
- *     - secondary: (optional) An array of local tasks (tabs).
- *
- * @ingroup themeable
- * @see menu_local_tasks()
- */
-function theme_menu_local_tasks(&$variables) {
-  $output = '';
-
-  if (!empty($variables['primary'])) {
-    $variables['primary']['#prefix'] = '<h2 class="visually-hidden">' . t('Primary tabs') . '</h2>';
-    $variables['primary']['#prefix'] .= '<ul class="tabs primary">';
-    $variables['primary']['#suffix'] = '</ul>';
-    $output .= drupal_render($variables['primary']);
-  }
-  if (!empty($variables['secondary'])) {
-    $variables['secondary']['#prefix'] = '<h2 class="visually-hidden">' . t('Secondary tabs') . '</h2>';
-    $variables['secondary']['#prefix'] .= '<ul class="tabs secondary">';
-    $variables['secondary']['#suffix'] = '</ul>';
-    $output .= drupal_render($variables['secondary']);
-  }
-
-  return $output;
-}
-
-/**
  * Sets (or gets) the active menu for the current page.
  *
  * The active menu for the page determines the active trail.
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 3dd8449..4343886 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2685,18 +2685,23 @@ function drupal_common_theme() {
     // From menu.inc.
     'menu_link' => array(
       'render element' => 'element',
+      'template' => 'menu-link',
     ),
     'menu_tree' => array(
       'render element' => 'tree',
+      'template' => 'menu-tree',
     ),
     'menu_local_task' => array(
       'render element' => 'element',
+      'template' => 'menu-local-task',
     ),
     'menu_local_action' => array(
       'render element' => 'element',
+      'template' => 'menu-local-action',
     ),
     'menu_local_tasks' => array(
       'variables' => array('primary' => array(), 'secondary' => array()),
+      'template' => 'menu-local-tasks',
     ),
     // From form.inc.
     'input' => array(
diff --git a/core/modules/system/css/system.theme.css b/core/modules/system/css/system.theme.css
index 4e83886..e7225b2 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -439,7 +439,7 @@ ul.links a.active {
 }
 
 /**
- * Markup generated by theme_menu_local_tasks().
+ * Markup generated by menu-local-tasks.html.twig.
  */
 div.tabs {
   margin: 1em 0;
diff --git a/core/modules/system/templates/menu-link.html.twig b/core/modules/system/templates/menu-link.html.twig
new file mode 100644
index 0000000..b629ca4
--- /dev/null
+++ b/core/modules/system/templates/menu-link.html.twig
@@ -0,0 +1,21 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a menu link and submenu.
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the wrapper element.
+ * - link: An HTML link element.
+ * - sub_menu: Rendered list item children of the element.
+ *
+ * Note: This template renders the content for each individual menu item in
+ * menu-local-tasks.html.twig.
+ *
+ * @see template_preprocess_menu_link()
+ *
+ * @ingroup themeable
+ */
+#}
+<li{{ attributes }}>
+  {{ link }}{{ sub_menu }}
+</li>
diff --git a/core/modules/system/templates/menu-local-action.html.twig b/core/modules/system/templates/menu-local-action.html.twig
new file mode 100644
index 0000000..eb02f42
--- /dev/null
+++ b/core/modules/system/templates/menu-local-action.html.twig
@@ -0,0 +1,14 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a single local action link.
+ *
+ * Available variables:
+ * - link: A rendered link element.
+ *
+ * @see template_preprocess_menu_local_action()
+ *
+ * @ingroup themeable
+ */
+#}
+<li>{{ link }}</li>
diff --git a/core/modules/system/templates/menu-local-task.html.twig b/core/modules/system/templates/menu-local-task.html.twig
new file mode 100644
index 0000000..20e19c0
--- /dev/null
+++ b/core/modules/system/templates/menu-local-task.html.twig
@@ -0,0 +1,22 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a local task link.
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the wrapper element.
+ * - link: The rendered link (<a> tag).
+ *
+ * Note: This template renders the content for each individual task item in
+ * menu-local-tasks.html.twig.
+ *
+ * @see template_preprocess_menu_local_task()
+ *
+ * @ingroup themeable
+ */
+#}
+{% spaceless %}
+  <li{{ attributes }}>
+    {{ link }}
+  </li>
+{% endspaceless %}
diff --git a/core/modules/system/templates/menu-local-tasks.html.twig b/core/modules/system/templates/menu-local-tasks.html.twig
new file mode 100644
index 0000000..511796d
--- /dev/null
+++ b/core/modules/system/templates/menu-local-tasks.html.twig
@@ -0,0 +1,25 @@
+{#
+/**
+ * @file
+ * Default theme implementation to display primary and secondary local tasks.
+ *
+ * Available variables:
+ * - primary_tasks: HTML list items representing primary tasks.
+ * - secondary_tasks: HTML list items representing primary tasks.
+ *
+ * Note: Each item for both sets of tasks can be individually themed in
+ * menu-local-task.html.twig.
+ *
+ * @see template_preprocess_menu_local_tasks()
+ *
+ * @ingroup themeable
+ */
+#}
+{% if primary %}
+  <h2 class="visually-hidden">{{ 'Primary tabs'|t }}</h2>
+  <ul class="tabs primary">{{ primary }}</ul>
+{% endif %}
+{% if secondary %}
+  <h2 class="visually-hidden">{{ 'Secondary tabs'|t }}</h2>
+  <ul class="tabs secondary">{{ secondary }}</ul>
+{% endif %}
diff --git a/core/modules/system/templates/menu-tree.html.twig b/core/modules/system/templates/menu-tree.html.twig
new file mode 100644
index 0000000..f056794
--- /dev/null
+++ b/core/modules/system/templates/menu-tree.html.twig
@@ -0,0 +1,19 @@
+{#
+/**
+ * @file
+ * Default theme implementation for the wrapper of a menu tree.
+ *
+ * Available variables:
+ * - tree: An HTML string containing the tree's items.
+ *
+ * Note: Each item in the menu tree can be individually themed in
+ * menu-link.html.twig.
+ *
+ * @see template_preprocess_menu_tree()
+ *
+ * @ingroup themeable
+ */
+#}
+<ul class="menu">
+  {{ tree }}
+</ul>
diff --git a/core/themes/bartik/bartik.theme b/core/themes/bartik/bartik.theme
index ab4683c..37f294d 100644
--- a/core/themes/bartik/bartik.theme
+++ b/core/themes/bartik/bartik.theme
@@ -161,20 +161,6 @@ function bartik_preprocess_node(&$variables) {
 }
 
 /**
- * Implements theme_menu_tree().
- */
-function bartik_menu_tree($variables) {
-  return '<ul class="menu clearfix">' . $variables['tree'] . '</ul>';
-}
-
-/**
- * Implements theme_menu_tree__shortcut_default() {
- */
-function bartik_menu_tree__shortcut_default($variables) {
-  return '<ul class="menu">' . $variables['tree'] . '</ul>';
-}
-
-/**
  * Implements theme_field__field_type().
  */
 function bartik_field__taxonomy_term_reference($variables) {
diff --git a/core/themes/bartik/templates/menu-tree--shortcut-default.html.twig b/core/themes/bartik/templates/menu-tree--shortcut-default.html.twig
new file mode 100644
index 0000000..19d95d2
--- /dev/null
+++ b/core/themes/bartik/templates/menu-tree--shortcut-default.html.twig
@@ -0,0 +1,19 @@
+{#
+/**
+ * @file
+ * Bartik's theme implementation for the wrapper of a shortcut menu tree.
+ *
+ * Available variables:
+ * - tree: An HTML string containing the tree's items.
+ *
+ * Note: Each item in the menu tree can be individually themed in
+ * menu-link.html.twig.
+ *
+ * @see template_preprocess_menu_tree()
+ *
+ * @ingroup themeable
+ */
+#}
+<ul class="menu">
+  {{ tree }}
+</ul>
diff --git a/core/themes/bartik/templates/menu-tree.html.twig b/core/themes/bartik/templates/menu-tree.html.twig
new file mode 100644
index 0000000..0ca902b
--- /dev/null
+++ b/core/themes/bartik/templates/menu-tree.html.twig
@@ -0,0 +1,19 @@
+{#
+/**
+ * @file
+ * Bartik's theme implementation for the wrapper of a menu tree.
+ *
+ * Available variables:
+ * - tree: An HTML string containing the tree's items.
+ *
+ * Note: Each item in the menu tree can be individually themed in
+ * menu-link.html.twig.
+ *
+ * @see template_preprocess_menu_tree()
+ *
+ * @ingroup themeable
+ */
+#}
+<ul class="menu clearfix">
+  {{ tree }}
+</ul>
