diff --git a/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php b/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
index 5d291db..458170b 100644
--- a/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
+++ b/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
@@ -33,6 +33,18 @@ public function query() {
    * {@inheritdoc}
    */
   public function prepareRow(Row $row) {
+    // This is a backward compatibility layer for the deprecated migrate source
+    // plugins d6_comment_variable and d6_comment_variable_per_comment_type.
+    if ($this->variableGet('comment_subject_field_' . $row->getSourceProperty('type'), 1)) {
+      // Comment subject visible.
+      $row->setSourceProperty('field_name', 'comment');
+      $row->setSourceProperty('comment_type', 'comment');
+    }
+    else {
+      $row->setSourceProperty('field_name', 'comment_no_subject');
+      $row->setSourceProperty('comment_type', 'comment_no_subject');
+    }
+
     // In D6, status=0 means published, while in D8 means the opposite.
     // See https://www.drupal.org/node/237636.
     $row->setSourceProperty('status', !$row->getSourceProperty('status'));
diff --git a/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php
new file mode 100644
index 0000000..2cf51ed
--- /dev/null
+++ b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariable.php
@@ -0,0 +1,114 @@
+<?php
+
+namespace Drupal\comment\Plugin\migrate\source\d6;
+
+@trigger_error('CommentVariable is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use \Drupal\node\Plugin\migrate\source\d6\ModeType instead.', E_USER_DEPRECATED);
+
+use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
+use Drupal\migrate\Plugin\migrate\source\DummyQueryTrait;
+
+/**
+ * @MigrateSource(
+ *   id = "d6_comment_variable",
+ *   source_module = "comment"
+ * )
+ *
+ * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
+ * \Drupal\node\Plugin\migrate\source\d6\NodeType instead.
+ */
+class CommentVariable extends DrupalSqlBase {
+
+  use DummyQueryTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function initializeIterator() {
+    return new \ArrayIterator($this->getCommentVariables());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count() {
+    return count($this->getCommentVariables());
+  }
+
+  /**
+   * Retrieves the values of the comment variables grouped by node type.
+   *
+   * @return array
+   */
+  protected function getCommentVariables() {
+    $comment_prefixes = array_keys($this->commentPrefixes());
+    $variables = [];
+    $node_types = $this->select('node_type', 'nt')
+      ->fields('nt', ['type'])
+      ->execute()
+      ->fetchCol();
+    foreach ($node_types as $node_type) {
+      foreach ($comment_prefixes as $prefix) {
+        $variables[] = $prefix . '_' . $node_type;
+      }
+    }
+    $return = [];
+    $values = $this->select('variable', 'v')
+      ->fields('v', ['name', 'value'])
+      ->condition('name', $variables, 'IN')
+      ->execute()
+      ->fetchAllKeyed();
+    foreach ($node_types as $node_type) {
+      foreach ($comment_prefixes as $prefix) {
+        $name = $prefix . '_' . $node_type;
+        if (isset($values[$name])) {
+          $return[$node_type][$prefix] = unserialize($values[$name]);
+        }
+      }
+    }
+    // The return key will not be used so move it inside the row. This could
+    // not be done sooner because otherwise empty rows would be created with
+    // just the node type in it.
+    foreach ($return as $node_type => $data) {
+      $return[$node_type]['node_type'] = $node_type;
+      $return[$node_type]['comment_type'] = empty($data['comment_subject_field']) ?
+        'comment_no_subject' : 'comment';
+    }
+    return $return;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return $this->commentPrefixes() + [
+      'node_type' => $this->t('The node type'),
+      'comment_type' => $this->t('The comment type'),
+    ];
+  }
+
+  /**
+   * Comment related data for fields.
+   */
+  protected function commentPrefixes() {
+    return [
+      'comment' => $this->t('Default comment setting'),
+      'comment_default_mode' => $this->t('Default display mode'),
+      'comment_default_order' => $this->t('Default display order'),
+      'comment_default_per_page' => $this->t('Default comments per page'),
+      'comment_controls' => $this->t('Comment controls'),
+      'comment_anonymous' => $this->t('Anonymous commenting'),
+      'comment_subject_field' => $this->t('Comment subject field'),
+      'comment_preview' => $this->t('Preview comment'),
+      'comment_form_location' => $this->t('Location of comment submission form'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids['node_type']['type'] = 'string';
+    return $ids;
+  }
+
+}
diff --git a/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariablePerCommentType.php b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariablePerCommentType.php
new file mode 100644
index 0000000..bfdb39c
--- /dev/null
+++ b/core/modules/comment/src/Plugin/migrate/source/d6/CommentVariablePerCommentType.php
@@ -0,0 +1,68 @@
+<?php
+
+namespace Drupal\comment\Plugin\migrate\source\d6;
+
+@trigger_error('CommentVariablePerCommentType is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use \Drupal\node\Plugin\migrate\source\d6\ModeType instead.', E_USER_DEPRECATED);
+
+/**
+ * @MigrateSource(
+ *   id = "d6_comment_variable_per_comment_type",
+ *   source_module = "comment"
+ * )
+ *
+ * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
+ * \Drupal\node\Plugin\migrate\source\d6\NodeType instead.
+ */
+class CommentVariablePerCommentType extends CommentVariable {
+
+  /**
+   * Retrieves the values of the comment variables grouped by comment type.
+   *
+   * @return array
+   */
+  protected function getCommentVariables() {
+    $node_types = parent::getCommentVariables();
+    // The return key used to separate comment types with hidden subject field.
+    $return = [];
+    foreach ($node_types as $node_type => $data) {
+      // Only 2 comment types depending on subject field visibility.
+      if (!empty($data['comment_subject_field'])) {
+        // Default label and description should be set in migration.
+        $return['comment'] = [
+          'comment_type' => 'comment',
+          'label' => $this->t('Default comments'),
+          'description' => $this->t('Allows commenting on content')
+        ];
+      }
+      else {
+        // Provide a special comment type with hidden subject field.
+        $return['comment_no_subject'] = [
+          'comment_type' => 'comment_no_subject',
+          'label' => $this->t('Comments without subject field'),
+          'description' => $this->t('Allows commenting on content, comments without subject field')
+        ];
+      }
+    }
+    return $return;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return [
+      'comment_type' => $this->t('The comment type'),
+      'label' => $this->t('The comment type label'),
+      'description' => $this->t('The comment type description'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids['comment_type']['type'] = 'string';
+    return $ids;
+  }
+
+}
diff --git a/core/modules/comment/src/Plugin/migrate/source/d7/CommentType.php b/core/modules/comment/src/Plugin/migrate/source/d7/CommentType.php
new file mode 100644
index 0000000..6890c6d
--- /dev/null
+++ b/core/modules/comment/src/Plugin/migrate/source/d7/CommentType.php
@@ -0,0 +1,103 @@
+<?php
+
+namespace Drupal\comment\Plugin\migrate\source\d7;
+
+@trigger_error('CommentType is deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use \Drupal\node\Plugin\migrate\source\d7\ModeType instead.', E_USER_DEPRECATED);
+
+use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
+use Drupal\migrate\Row;
+use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
+
+/**
+ * Drupal 7 comment type source from database.
+ *
+ * @MigrateSource(
+ *   id = "d7_comment_type",
+ *   source_module = "comment"
+ * )
+ *
+ * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
+ * \Drupal\node\Plugin\migrate\source\d7\NodeType instead.
+ */
+class CommentType extends DrupalSqlBase {
+
+  /**
+   * A map of D7 node types to their labels.
+   *
+   * @var string[]
+   */
+  protected $nodeTypes = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query() {
+    return $this->select('field_config_instance', 'fci')
+      ->distinct()
+      ->fields('fci', ['bundle'])
+      ->condition('fci.entity_type', 'comment');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function initializeIterator() {
+    $this->nodeTypes = $this->select('node_type', 'nt')
+      ->fields('nt', ['type', 'name'])
+      ->execute()
+      ->fetchAllKeyed();
+
+    return parent::initializeIterator();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepareRow(Row $row) {
+    $node_type = substr($row->getSourceProperty('bundle'), 13);
+    $row->setSourceProperty('node_type', $node_type);
+
+    $row->setSourceProperty('default_mode', $this->variableGet("comment_default_mode_$node_type", 1));
+    $row->setSourceProperty('per_page', $this->variableGet("comment_default_per_page_$node_type", 50));
+    $row->setSourceProperty('anonymous', $this->variableGet("comment_anonymous_$node_type", FALSE));
+    $row->setSourceProperty('form_location', $this->variableGet("comment_form_location_$node_type", CommentItemInterface::FORM_BELOW));
+    $row->setSourceProperty('preview', $this->variableGet("comment_preview_$node_type", TRUE));
+    $row->setSourceProperty('subject', $this->variableGet("comment_subject_field_$node_type", TRUE));
+
+    $label = $this->t('@node_type comment', [
+      '@node_type' => $this->nodeTypes[$node_type],
+    ]);
+    $row->setSourceProperty('label', $label);
+
+    return parent::prepareRow($row);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return [
+      'label' => $this->t('The label of the comment type.'),
+      'bundle' => $this->t('Bundle ID of the comment type.'),
+      'node_type' => $this->t('The node type to which this comment type is attached.'),
+      'default_mode' => $this->t('Default comment mode.'),
+      'per_page' => $this->t('Number of comments visible per page.'),
+      'anonymous' => $this->t('Whether anonymous comments are allowed.'),
+      'form_location' => $this->t('Location of the comment form.'),
+      'preview' => $this->t('Whether previews are enabled for the comment type.'),
+      'subject' => $this->t('Whether a subject field is enabled for the comment type.'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    return [
+      'bundle' => [
+        'type' => 'string',
+      ],
+    ];
+  }
+
+}
diff --git a/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php
new file mode 100644
index 0000000..dd1b1fd
--- /dev/null
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariablePerCommentTypeTest.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d6;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests comment variable per comment type source plugin.
+ *
+ * @covers \Drupal\comment\Plugin\migrate\source\d6\CommentVariablePerCommentType
+ * @group comment
+ */
+class CommentVariablePerCommentTypeTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['comment', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['source_data']['node_type'] = [
+      [
+        'type' => 'page',
+      ],
+      [
+        'type' => 'story',
+      ],
+    ];
+
+    $tests[0]['source_data']['variable'] = [
+      [
+        'name' => 'comment_subject_field_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_subject_field_story',
+        'value' => serialize(0),
+      ],
+    ];
+
+    // The expected results.
+    // Each result will also include a label and description, but those are
+    // static values set by the source plugin and don't need to be asserted.
+    $tests[0]['expected_data'] = [
+      [
+        'comment_type' => 'comment',
+      ],
+      [
+        'comment_type' => 'comment_no_subject',
+      ],
+    ];
+
+    return $tests;
+  }
+
+}
diff --git a/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php
new file mode 100644
index 0000000..a84c776
--- /dev/null
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d6/CommentVariableTest.php
@@ -0,0 +1,92 @@
+<?php
+
+namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d6;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests d6_comment_variable source plugin.
+ *
+ * @covers \Drupal\comment\Plugin\migrate\source\d6\CommentVariable
+ * @group comment
+ */
+class CommentVariableTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['comment', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['source_data']['node_type'] = [
+      [
+        'type' => 'page',
+      ],
+    ];
+
+    $tests[0]['source_data']['variable'] = [
+      [
+        'name' => 'comment_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_default_mode_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_default_order_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_default_per_page_page',
+        'value' => serialize(50),
+      ],
+      [
+        'name' => 'comment_controls_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_anonymous_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_subject_field_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_preview_page',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_form_location_page',
+        'value' => serialize(1),
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'comment' => '1',
+        'comment_default_mode' => '1',
+        'comment_default_order' => '1',
+        'comment_default_per_page' => '50',
+        'comment_controls' => '1',
+        'comment_anonymous' => '1',
+        'comment_subject_field' => '1',
+        'comment_preview' => '1',
+        'comment_form_location' => '1',
+        'node_type' => 'page',
+        'comment_type' => 'comment',
+      ],
+    ];
+
+    return $tests;
+  }
+
+}
diff --git a/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php
new file mode 100644
index 0000000..11f3db5
--- /dev/null
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTypeTest.php
@@ -0,0 +1,99 @@
+<?php
+
+namespace Drupal\Tests\comment\Kernel\Plugin\migrate\source\d7;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests D7 comment type source plugin.
+ *
+ * @covers \Drupal\comment\Plugin\migrate\source\d7\CommentType
+ * @group comment
+ */
+class CommentTypeTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['comment', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['source_data']['node_type'] = [
+      [
+        'type' => 'article',
+        'name' => 'Article',
+        'base' => 'node_content',
+        'module' => 'node',
+        'description' => 'Use <em>articles</em> for time-sensitive content like news, press releases or blog posts.',
+        'help' => 'Help text for articles',
+        'has_title' => '1',
+        'title_label' => 'Title',
+        'custom' => '1',
+        'modified' => '1',
+        'locked' => '0',
+        'disabled' => '0',
+        'orig_type' => 'article',
+      ],
+    ];
+    $tests[0]['source_data']['field_config_instance'] = [
+      [
+        'id' => '14',
+        'field_id' => '1',
+        'field_name' => 'comment_body',
+        'entity_type' => 'comment',
+        'bundle' => 'comment_node_article',
+        'data' => 'a:0:{}',
+        'deleted' => '0',
+      ],
+    ];
+    $tests[0]['source_data']['variable'] = [
+      [
+        'name' => 'comment_default_mode_article',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_per_page_article',
+        'value' => serialize(50),
+      ],
+      [
+        'name' => 'comment_anonymous_article',
+        'value' => serialize(0),
+      ],
+      [
+        'name' => 'comment_form_location_article',
+        'value' => serialize(1),
+      ],
+      [
+        'name' => 'comment_preview_article',
+        'value' => serialize(0),
+      ],
+      [
+        'name' => 'comment_subject_article',
+        'value' => serialize(1),
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'bundle' => 'comment_node_article',
+        'node_type' => 'article',
+        'default_mode' => '1',
+        'per_page' => '50',
+        'anonymous' => '0',
+        'form_location' => '1',
+        'preview' => '0',
+        'subject' => '1',
+        'label' => 'Article comment',
+      ],
+    ];
+    return $tests;
+  }
+
+}