diff --git a/core/modules/comment/comment.api.php b/core/modules/comment/comment.api.php
index 793d9ad6373382401715c3c2f8b7d6262b91e050..a27899e7755a0e0d468291fd8408da4219313f12 100644
--- a/core/modules/comment/comment.api.php
+++ b/core/modules/comment/comment.api.php
@@ -113,8 +113,7 @@ function hook_comment_view(\Drupal\comment\Plugin\Core\Entity\Comment $comment,
  * If the module wishes to act on the rendered HTML of the comment rather than
  * the structured content array, it may use this hook to add a #post_render
  * callback. Alternatively, it could also implement hook_preprocess_HOOK() for
- * comment.tpl.php. See drupal_render() and theme() documentation respectively
- * for details.
+ * comment.html.twig. See drupal_render() documentation for details.
  *
  * @param $build
  *   A renderable array representing the comment.
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 0c2cd55a1c40a0998a289dc2ecc6059170af205c..807b672c7fa59d80f26f56536052d3adc2215e96 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -1553,9 +1553,14 @@ function comment_prepare_author(Comment $comment) {
 }
 
 /**
- * Preprocesses variables for comment.tpl.php.
+ * Prepares variables for comment templates.
  *
- * @see comment.tpl.php
+ * Default template: comment.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - elements: An associative array containing the comment and node objects.
+ *     Array keys: #comment, #node.
  */
 function template_preprocess_comment(&$variables) {
   $comment = $variables['elements']['#comment'];
@@ -1564,6 +1569,7 @@ function template_preprocess_comment(&$variables) {
   $variables['node'] = $node;
 
   $account = comment_prepare_author($comment);
+  // @todo Do not call theme() here. We do this for purposes of t().
   $variables['author'] = theme('username', array('account' => $account));
   $variables['new'] = $comment->new->value ? t('new') : '';
   $variables['created'] = format_date($comment->created->value);
@@ -1583,6 +1589,7 @@ function template_preprocess_comment(&$variables) {
   else {
     $variables['user_picture'] = array();
   }
+
   if (config('user.settings')->get('signatures') && !empty($account->signature)) {
     $variables['signature'] = check_markup($account->signature, $account->signature_format, '', TRUE) ;
   }
@@ -1602,6 +1609,7 @@ function template_preprocess_comment(&$variables) {
     $comment_parent = $comment->pid->entity;
     $account_parent = comment_prepare_author($comment_parent);
     $variables['parent_comment'] = $comment_parent;
+    // @todo Do not call theme() here. We do this for purposes of t().
     $variables['parent_author'] = theme('username', array('account' => $account_parent));
     $variables['parent_created'] = format_date($comment_parent->created->value);
     // Avoid calling format_date() twice on the same timestamp.
@@ -1664,6 +1672,10 @@ function template_preprocess_comment(&$variables) {
       $variables['attributes']['class'][] = 'by-viewer';
     }
   }
+  // Add clearfix class.
+  $variables['attributes']['class'][] = 'clearfix';
+
+  $variables['content_attributes']['class'][] = 'content';
 }
 
 /**
@@ -1714,19 +1726,31 @@ function theme_comment_post_forbidden($variables) {
 }
 
 /**
- * Preprocesses variables for comment-wrapper.tpl.php.
+ * Prepares variables for comment wrapper templates.
+ *
+ * Default template: comment-wrapper.html.twig.
  *
- * @see comment-wrapper.tpl.php
+ * @param array $variables
+ *   An associative array containing:
+ *   - content: An associative array containing render arrays for the list of
+ *     comments, and the comment form. Array keys: comments, comment_form.
  */
 function template_preprocess_comment_wrapper(&$variables) {
   // Provide contextual information.
   $variables['node'] = $variables['content']['#node'];
   $variables['display_mode'] = variable_get('comment_default_mode_' . $variables['node']->type, COMMENT_MODE_THREADED);
+
   // The comment form is optional and may not exist.
   $variables['content'] += array('comment_form' => array());
 
+  $variables['attributes']['id'] = 'comments';
+
   // Add a comment wrapper class.
   $variables['attributes']['class'][] = 'comment-wrapper';
+
+  // Create separate variables for the comments and comment form.
+  $variables['comments'] = $variables['content']['comments'];
+  $variables['form'] = $variables['content']['comment_form'];
 }
 
 /**
diff --git a/core/modules/comment/templates/comment-wrapper.html.twig b/core/modules/comment/templates/comment-wrapper.html.twig
new file mode 100644
index 0000000000000000000000000000000000000000..dbf37cd9030c3abd7b868cf0f92bca24998d75cb
--- /dev/null
+++ b/core/modules/comment/templates/comment-wrapper.html.twig
@@ -0,0 +1,53 @@
+{#
+/**
+ * @file
+ * Default theme implementation for a comments container.
+ *
+ * Available variables:
+ * - comments: List of comments rendered through comment.html.twig.
+ * - form: The 'Add new comment' form.
+ * - content: The content-related elements for the comment display. Use
+ *   'content' to print them all, or print a subset such as
+ *   'content.comment_form'.
+ * - attributes: Remaining HTML attributes for the containing element.
+ *   It includes the 'class' information, which includes:
+ *   - comment-wrapper: The current template type, i.e., "theming hook".
+ *   - title_prefix: Additional output populated by modules, intended to be
+ *     displayed in front of the main title tag that appears in the template.
+ *   - title_suffix: Additional title output populated by modules, intended to
+ *     be displayed after the main title tag that appears in the template.
+ *
+ * The following variables are provided for contextual information.
+ * - node: The node entity to which the comments belong.
+ * - display_mode: The display mode for the comment listing, flat or threaded.
+ *   The constants below show the possible values and should be used for
+ *   comparison, as in the following example:
+ *   @code
+ *   {% if display_mode is constant('COMMENT_MODE_THREADED') %}
+ *     <h3>{{ 'These comments are displayed in a threaded list.'|t }}</h3>
+ *   {% endif %}
+ *   @endcode
+ *   - COMMENT_MODE_FLAT
+ *   - COMMENT_MODE_THREADED
+ *
+ * @see template_preprocess()
+ * @see template_preprocess_comment_wrapper()
+ *
+ * @ingroup themeable
+ */
+#}
+<section{{ attributes }}>
+  {% if comments and node.type != 'forum' %}
+    {{ title_prefix }}
+    <h2 class="title">{{ 'Comments'|t }}</h2>
+    {{ title_suffix }}
+  {% endif %}
+
+  {{ comments }}
+
+  {% if form %}
+    <h2 class="title comment-form">{{ 'Add new comment'|t }}</h2>
+    {{ form }}
+  {% endif %}
+
+</section>
diff --git a/core/modules/comment/templates/comment-wrapper.tpl.php b/core/modules/comment/templates/comment-wrapper.tpl.php
deleted file mode 100644
index ac1c27f94f99297c67afd249e275598fdc49af15..0000000000000000000000000000000000000000
--- a/core/modules/comment/templates/comment-wrapper.tpl.php
+++ /dev/null
@@ -1,48 +0,0 @@
-<?php
-
-/**
- * @file
- * Provides an HTML container for comments.
- *
- * Available variables:
- * - $content: The array of content-related elements for the node. Use
- *   render($content) to print them all, or
- *   print a subset such as render($content['comment_form']).
- * - $attributes: An instance of Attributes class that can be manipulated as an
- *    array and printed as a string.
- *    It includes the 'class' information, which includes:
- *   - comment-wrapper: The current template type, i.e., "theming hook".
- * - $title_prefix (array): An array containing additional output populated by
- *   modules, intended to be displayed in front of the main title tag that
- *   appears in the template.
- * - $title_suffix (array): An array containing additional output populated by
- *   modules, intended to be displayed after the main title tag that appears in
- *   the template.
- *
- * The following variables are provided for contextual information.
- * - $node: Node entity the comments are attached to.
- * The constants below the variables show the possible values and should be
- * used for comparison.
- * - $display_mode
- *   - COMMENT_MODE_FLAT
- *   - COMMENT_MODE_THREADED
- *
- * @see template_preprocess_comment_wrapper()
- *
- * @ingroup themeable
- */
-?>
-<section id="comments" <?php print $attributes; ?>>
-  <?php if ($content['comments'] && $node->type != 'forum'): ?>
-    <?php print render($title_prefix); ?>
-    <h2 class="title"><?php print t('Comments'); ?></h2>
-    <?php print render($title_suffix); ?>
-  <?php endif; ?>
-
-  <?php print render($content['comments']); ?>
-
-  <?php if ($content['comment_form']): ?>
-    <h2 class="title comment-form"><?php print t('Add new comment'); ?></h2>
-    <?php print render($content['comment_form']); ?>
-  <?php endif; ?>
-</section>
diff --git a/core/modules/comment/templates/comment.html.twig b/core/modules/comment/templates/comment.html.twig
new file mode 100644
index 0000000000000000000000000000000000000000..4b441dd24ef19c68a7f7601b00163379d884b64c
--- /dev/null
+++ b/core/modules/comment/templates/comment.html.twig
@@ -0,0 +1,106 @@
+{#
+/**
+ * @file
+ * Default theme implementation for comments.
+ *
+ * Available variables:
+ * - author: Comment author. Can be a link or plain text.
+ * - content: The content-related items for the comment display. Use
+ *   {{ content }} to print them all, or print a subset such as
+ *   {{ content.field_example }}. Use hide(content.field_example) to temporarily
+ *   suppress the printing of a given element.
+ * - created: Formatted date and time for when the comment was created.
+ *   Preprocess functions can reformat it by calling format_date() with the
+ *   desired parameters on the 'comment.created' variable.
+ * - changed: Formatted date and time for when the comment was last changed.
+ *   Preprocess functions can reformat it by calling format_date() with the
+ *   desired parameters on the 'comment.changed' variable.
+ * - new: New comment marker.
+ * - permalink: Comment permalink.
+ * - submitted: Submission information created from author and created
+ *   during template_preprocess_comment().
+ * - user_picture: The comment author's profile picture.
+ * - signature: The comment author's signature.
+ * - status: Comment status. Possible values are:
+ *   unpublished, published, or preview.
+ * - title: Comment title, linked to the comment.
+ * - attributes.class: List of classes that can be used to style contextually
+ *   through CSS. The default values can be one or more of the following:
+ *   - comment: The current template type; e.g., 'theming hook'.
+ *   - by-anonymous: Comment by an unregistered user.
+ *   - by-node-author: Comment by the author of the parent node.
+ *   - preview: When previewing a new or edited comment.
+ *   The following applies only to viewers who are registered users:
+ *   - unpublished: An unpublished comment visible only to administrators.
+ *   - by-viewer: Comment by the user currently viewing the page.
+ *   - new: New comment since the last visit.
+ * - title_prefix: Additional output populated by modules, intended to be
+ *   displayed in front of the main title tag that appears in the template.
+ * - title_suffix: Additional output populated by modules, intended to be
+ *   displayed after the main title tag that appears in the template.
+ * - content_attributes: List of classes for the styling of the comment content.
+ *
+ * These variables are provided to give context about the parent comment (if
+ * any):
+ * - comment_parent: Full parent comment entity (if any).
+ * - parent_author: Equivalent to author for the parent comment.
+ * - parent_created: Equivalent to created for the parent comment.
+ * - parent_changed: Equivalent to changed for the parent comment.
+ * - parent_title: Equivalent to title for the parent comment.
+ * - parent_permalink: Equivalent to permalink for the parent comment.
+ * - parent: A text string of parent comment submission information created from
+ *   'parent_author' and 'parent_created' during template_preprocess_comment().
+ *   This information is presented to help screen readers follow lengthy
+ *   discussion threads. You can hide this from sighted users using the class
+ *   element-invisible.
+ *
+ * These two variables are provided for context:
+ * - comment: Full comment object.
+ * - node: Node entity the comments are attached to.
+ *
+ * @see template_preprocess()
+ * @see template_preprocess_comment()
+ *
+ * @ingroup themeable
+ */
+#}
+<article{{ attributes }}>
+  {{ title_prefix }}
+
+  {% if new %}
+    <mark class="new">{{ new }}</mark>
+  {% endif %}
+
+  <h3{{ title_attributes }}>{{ title }}</h3>
+
+  {{ title_suffix }}
+
+  <footer>
+    {{ user_picture }}
+    <p class="submitted">{{ submitted }}</p>
+
+    {#
+      Indicate the semantic relationship between parent and child comments
+      for accessibility. The list is difficult to navigate in a screen
+      reader without this information.
+    #}
+    {% if parent %}
+      <p class="parent element-invisible">{{ parent }}</p>
+    {% endif %}
+
+    {{ permalink }}
+  </footer>
+
+  <div{{ content_attributes }}>
+    {# We hide the links now so that we can render them later. #}
+    {% hide(content.links) %}
+    {{ content }}
+
+    {% if signature %}
+      <div class="user-signature">
+        {{ signature }}
+      </div>
+    {% endif %}
+  </div>
+  {{ content.links }}
+</article>
diff --git a/core/modules/comment/templates/comment.tpl.php b/core/modules/comment/templates/comment.tpl.php
deleted file mode 100644
index 5a8a37e50284c1b64345b2d736edbaa35ec2dc3a..0000000000000000000000000000000000000000
--- a/core/modules/comment/templates/comment.tpl.php
+++ /dev/null
@@ -1,110 +0,0 @@
-<?php
-
-/**
- * @file
- * Default theme implementation for comments.
- *
- * Available variables:
- * - $author: Comment author. Can be link or plain text.
- * - $content: An array of comment items. Use render($content) to print them
- *   all, or print a subset such as render($content['field_example']). Use
- *   hide($content['field_example']) to temporarily suppress the printing of a
- *   given element.
- * - $created: Formatted date and time for when the comment was created.
- *   Preprocess functions can reformat it by calling format_date() with the
- *   desired parameters on the $comment->created variable.
- * - $changed: Formatted date and time for when the comment was last changed.
- *   Preprocess functions can reformat it by calling format_date() with the
- *   desired parameters on the $comment->changed variable.
- * - $new: New comment marker.
- * - $permalink: Comment permalink.
- * - $submitted: Submission information created from $author and $created during
- *   template_preprocess_comment().
- * - $user_picture: The comment author's picture. Use render($user_picture) to
- *   print it.
- * - $signature: Authors signature.
- * - $status: Comment status. Possible values are:
- *   unpublished, published, or preview.
- * - $title: Linked title.
- * - $attributes: An instance of Attributes class that can be manipulated as an
- *    array and printed as a string.
- *    It includes the 'class' information, which includes:
- *   - comment: The current template type; e.g., 'theming hook'.
- *   - by-anonymous: Comment by an unregistered user.
- *   - by-node-author: Comment by the author of the parent node.
- *   - preview: When previewing a new or edited comment.
- *   The following applies only to viewers who are registered users:
- *   - unpublished: An unpublished comment visible only to administrators.
- *   - by-viewer: Comment by the user currently viewing the page.
- *   - new: New comment since the last visit.
- * - $title_prefix (array): An array containing additional output populated by
- *   modules, intended to be displayed in front of the main title tag that
- *   appears in the template.
- * - $title_suffix (array): An array containing additional output populated by
- *   modules, intended to be displayed after the main title tag that appears in
- *   the template.
- *
- * These variables are provided to give context about the parent comment (if
- * any):
- * - $comment_parent: Full parent comment object (if any).
- * - $parent_author: Equivalent to $author for the parent comment.
- * - $parent_created: Equivalent to $created for the parent comment.
- * - $parent_changed: Equivalent to $changed for the parent comment.
- * - $parent_title: Equivalent to $title for the parent comment.
- * - $parent_permalink: Equivalent to $permalink for the parent comment.
- * - $parent: A text string of parent comment submission information created
- *   from $parent_author and $parent_created during
- *   template_preprocess_comment(). This information is presented to help
- *   screen readers follow lengthy discussion threads. You can hide this from
- *   sighted users using the class element-invisible.
- *
- * These two variables are provided for context:
- * - $comment: Full comment object.
- * - $node: Node entity the comments are attached to.
- *
- * @see template_preprocess()
- * @see template_preprocess_comment()
- * @see template_process()
- * @see theme_comment()
- *
- * @ingroup themeable
- */
-?>
-<article class="<?php print $attributes['class']; ?> clearfix"<?php print $attributes; ?>>
-
-  <?php print render($title_prefix); ?>
-  <?php if ($new): ?>
-    <mark class="new"><?php print $new; ?></mark>
-  <?php endif; ?>
-  <h3<?php print $title_attributes; ?>><?php print $title; ?></h3>
-  <?php print render($title_suffix); ?>
-
-  <footer>
-    <?php print render($user_picture); ?>
-    <p class="submitted"><?php print $submitted; ?></p>
-    <?php
-      // Indicate the semantic relationship between parent and child comments
-      // for accessibility. The list is difficult to navigate in a screen
-      // reader without this information.
-      if ($parent):
-    ?>
-      <p class="parent element-invisible"><?php print $parent; ?></p>
-    <?php endif; ?>
-    <?php print $permalink; ?>
-  </footer>
-
-  <div class="content"<?php print $content_attributes; ?>>
-    <?php
-      // We hide the links now so that we can render them later.
-      hide($content['links']);
-      print render($content);
-    ?>
-    <?php if ($signature): ?>
-    <div class="user-signature">
-      <?php print $signature; ?>
-    </div>
-    <?php endif; ?>
-  </div>
-
-  <?php print render($content['links']) ?>
-</article>
diff --git a/core/modules/rdf/rdf.module b/core/modules/rdf/rdf.module
index a2f74a33e8780894ed08463b81ffbc3588e31d41..3783f6bcaadcce310f9f094d0dd86b9ee977ded3 100644
--- a/core/modules/rdf/rdf.module
+++ b/core/modules/rdf/rdf.module
@@ -701,7 +701,7 @@ function rdf_preprocess_username(&$variables) {
 }
 
 /**
- * Implements hook_preprocess_HOOK() for comment.tpl.php.
+ * Implements hook_preprocess_HOOK() for comment.html.twig.
  */
 function rdf_preprocess_comment(&$variables) {
   $comment = $variables['comment'];
@@ -848,7 +848,7 @@ function rdf_preprocess_image(&$variables) {
  *     - variable_name: The name of the variable by which the template will
  *       refer to this content. Each template file has documentation about
  *       the variables it uses. For example, if this function is called in
- *       preparing the $author variable for comment.tpl.php, then the
+ *       preparing the $author variable for comment.html.twig, then the
  *       'variable_name' is 'author'.
  *     - variables: The full array of variables about to be passed to the
  *       template.