diff --git a/core/modules/comment/comment.admin.inc b/core/modules/comment/comment.admin.inc
index 2013de8..cf6191a 100644
--- a/core/modules/comment/comment.admin.inc
+++ b/core/modules/comment/comment.admin.inc
@@ -39,7 +39,6 @@ function comment_admin($type = 'new') {
  * @see comment_admin()
  * @see comment_admin_overview_validate()
  * @see comment_admin_overview_submit()
- * @see theme_comment_admin_overview()
  */
 function comment_admin_overview($form, &$form_state, $arg) {
   // Build an 'Update options' form.
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 9f8b282..a71fad2 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -175,20 +175,15 @@ function comment_theme() {
   return array(
     'comment_block' => array(
       'variables' => array('number' => NULL),
-    ),
-    'comment_preview' => array(
-      'variables' => array('comment' => NULL),
+      'template' => 'comment-block',
     ),
     'comment' => array(
-      'template' => 'comment',
       'render element' => 'elements',
-    ),
-    'comment_post_forbidden' => array(
-      'variables' => array('commented_entity' => NULL, 'field_name' => 'comment'),
+      'template' => 'comment',
     ),
     'comment_wrapper' => array(
-      'template' => 'comment-wrapper',
       'render element' => 'content',
+      'template' => 'comment-wrapper',
     ),
   );
 }
@@ -440,26 +435,23 @@ function comment_new_page_count($num_comments, $new_replies, EntityInterface $en
 }
 
 /**
- * Returns HTML for a list of recent comments.
+ * Prepares variables for comment block templates.
  *
- * @ingroup themeable
+ * Default template: comment-block.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - number: The number of recent comments to display.
  */
-function theme_comment_block($variables) {
-  $items = array();
+function template_preprocess_comment_block(&$variables) {
+  $variables['comments'] = array();
   $number = $variables['number'];
   foreach (comment_get_recent($number) as $comment) {
-    $items[] = l($comment->subject, 'comment/' . $comment->cid, array('fragment' => 'comment-' . $comment->cid)) . '&nbsp;<span>' . t('@time ago', array('@time' => format_interval(REQUEST_TIME - $comment->changed))) . '</span>';
-  }
-
-  if ($items) {
-    $item_list = array(
-      '#theme' => 'item_list',
-      '#items' => $items,
+    $variables['comments'][] = array(
+      'data' => $comment,
+      'link' => l($comment->subject, 'comment/' . $comment->cid, array('fragment' => 'comment-' . $comment->cid)),
+      'time' => format_interval(REQUEST_TIME - $comment->changed),
     );
-    return drupal_render($item_list);
-  }
-  else {
-    return t('No comments available.');
   }
 }
 
@@ -541,13 +533,8 @@ function comment_entity_view(EntityInterface $entity, EntityDisplay $display, $v
             }
           }
           else {
-            $comment_post_forbidden = array(
-              '#theme' => 'comment_post_forbidden',
-              '#commented_entity' => $entity,
-              '#field_name' => $field_name,
-            );
             $links['comment-forbidden'] = array(
-              'title' => drupal_render($comment_post_forbidden),
+              'title' => comment_forbidden_message($entity, $field_name),
               'html' => TRUE,
             );
           }
@@ -576,13 +563,8 @@ function comment_entity_view(EntityInterface $entity, EntityDisplay $display, $v
             }
           }
           else {
-            $comment_post_forbidden = array(
-              '#theme' => 'comment_post_forbidden',
-              '#commented_entity' => $entity,
-              '#field_name' => $field_name,
-            );
             $links['comment-forbidden'] = array(
-              'title' => drupal_render($comment_post_forbidden),
+              'title' => comment_forbidden_message($entity, $field_name),
               'html' => TRUE,
             );
           }
@@ -1512,19 +1494,23 @@ function template_preprocess_comment(&$variables) {
 }
 
 /**
- * Returns HTML for a "you can't post comments" notice.
+ * Provides a message if posting comments is forbidden.
  *
- * @param $variables
- *   An associative array containing:
- *   - commented_entity: The entity to which comments are attached to.
- *   - field_name: The comment field.
+ * If authenticated users can post comments, a message is returned that prompts
+ * the anonymous user to log in (or register, if applicable) that redirects to
+ * entity comment form. Otherwise, no message is returned.
  *
- * @ingroup themeable
+ * @param \Drupal\Core\Entity\EntityInterface $entity
+ *   The entity to which comments are attached to.
+ * @param string $field_name
+ *   The field name on the entity to which comments are attached to.
+ *
+ * @return
+ *   HTML for a "you can't post comments" notice.
  */
-function theme_comment_post_forbidden($variables) {
-  $entity = $variables['commented_entity'];
-  $field_name = $variables['field_name'];
-  global $user;
+function comment_forbidden_message(EntityInterface $entity, $field_name) {
+
+  $user = \Drupal::currentUser();
 
   // Since this is expensive to compute, we cache it so that a page with many
   // comments only has to query the database once for all the links.
diff --git a/core/modules/comment/templates/comment-block.html.twig b/core/modules/comment/templates/comment-block.html.twig
new file mode 100644
index 0000000..13f7816
--- /dev/null
+++ b/core/modules/comment/templates/comment-block.html.twig
@@ -0,0 +1,24 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a list of recent comments.
+ *
+ * Available variables:
+ * - comments: A list of recent comments.
+ *
+ * @see template_preprocess_comment_block()
+ *
+ * @ingroup themeable
+ */
+#}
+{% if comments %}
+  <ul>
+    {% for comment in comments %}
+      <li class="{{ cycle(['odd', 'even'], loop.index) }}{{ loop.first ? ' first' }}{{ loop.last ? ' last' }}">
+        {{ comment.link }}&nbsp;<span>{{ '@time ago'|t({ '@time' : comment.time }) }}</span>
+      </li>
+    {% endfor %}
+  </ul>
+{% else %}
+  {{ 'No comments available.'|t }}
+{% endif %}