diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 416571d..6753f28 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -166,11 +166,8 @@ function aggregator_menu() {
   );
   $items['aggregator/categories/%aggregator_category/categorize'] = array(
     'title' => 'Categorize',
-    'page callback' => 'drupal_get_form',
-    'page arguments' => array('aggregator_page_category_form', 2),
-    'access arguments' => array('administer news feeds'),
     'type' => MENU_LOCAL_TASK,
-    'file' => 'aggregator.pages.inc',
+    'route_name' => 'aggregator_categorize_category_form',
   );
   $items['aggregator/categories/%aggregator_category/configure'] = array(
     'title' => 'Configure',
@@ -195,11 +192,8 @@ function aggregator_menu() {
   );
   $items['aggregator/sources/%aggregator_feed/categorize'] = array(
     'title' => 'Categorize',
-    'page callback' => 'drupal_get_form',
-    'page arguments' => array('aggregator_page_source_form', 2),
-    'access arguments' => array('administer news feeds'),
+    'route_name' => 'aggregator_categorize_feed_form',
     'type' => MENU_LOCAL_TASK,
-    'file' => 'aggregator.pages.inc',
   );
   $items['aggregator/sources/%aggregator_feed/configure'] = array(
     'title' => 'Configure',
diff --git a/core/modules/aggregator/aggregator.pages.inc b/core/modules/aggregator/aggregator.pages.inc
index 0fa2bd8..20b145f 100644
--- a/core/modules/aggregator/aggregator.pages.inc
+++ b/core/modules/aggregator/aggregator.pages.inc
@@ -30,23 +30,6 @@ function aggregator_page_source(Feed $feed) {
 }
 
 /**
- * Form constructor to show all items captured from a feed.
- *
- * @param $feed
- *   The feed for which to list all of the aggregated items.
- *
- * @return string
- *   The rendered list of items for the feed.
- *
- * @see aggregator_menu()
- * @see aggregator_page_source()
- * @ingroup forms
- */
-function aggregator_page_source_form($form, $form_state, $feed) {
-  return aggregator_page_source($feed);
-}
-
-/**
  * Form constructor to list items aggregated in a category.
  *
  * @param $category
@@ -69,23 +52,6 @@ function aggregator_page_category($category) {
 }
 
 /**
- * Form constructor to list items aggregated in a category.
- *
- * @param $category
- *   The category for which to list all of the aggregated items.
- *
- * @return string
- *   The rendered list of items for the feed.
- *
- * @see aggregator_menu()
- * @see aggregator_page_category()
- * @ingroup forms
- */
-function aggregator_page_category_form($form, $form_state, $category) {
-  return aggregator_page_category($category);
-}
-
-/**
  * Loads and optionally filters feed items.
  *
  * @param string $type
@@ -144,111 +110,17 @@ function aggregator_load_feed_items($type, $data = NULL, $limit = 20) {
  *   The rendered list of items for the feed.
  */
 function _aggregator_page_list($items, $op, $feed_source = '') {
-  if (user_access('administer news feeds') && ($op == 'categorize')) {
-    // Get form data.
-    $build = aggregator_categorize_items($items, $feed_source);
-  }
-  else {
-    // Assemble output.
-    $build = array(
-      '#type' => 'container',
-      '#attributes' => array('class' => array('aggregator-wrapper')),
-    );
-    $build['feed_source'] = is_array($feed_source) ? $feed_source : array('#markup' => $feed_source);
-    if ($items) {
-      $build['items'] = entity_view_multiple($items, 'default');
-      $build['pager'] = array('#theme' => 'pager');
-    }
-  }
-
-  return $build;
-}
-
-/**
- * Form constructor to build the page list form.
- *
- * @param array $items
- *   An array of the feed items.
- * @param string $feed_source
- *   (optional) The feed source URL. Defaults to an empty string.
- *
- * @return array
- *   An array of FAPI elements.
- *
- * @see aggregator_categorize_items_submit()
- * @see theme_aggregator_categorize_items()
- * @ingroup forms
- */
-function aggregator_categorize_items($items, $feed_source = '') {
-  $form['#submit'][] = 'aggregator_categorize_items_submit';
-  $form['feed_source'] = array(
-    '#value' => $feed_source,
-  );
-  $categories = array();
-  $done = FALSE;
-
-  $form['items'] = array(
-    '#type' => 'table',
-    '#header' => array('', t('Categorize')),
+  // Assemble output.
+  $build = array(
+    '#type' => 'container',
+    '#attributes' => array('class' => array('aggregator-wrapper')),
   );
-  if ($items && $form_items = entity_view_multiple($items, 'default')) {
-    foreach (element_children($form_items) as $iid) {
-      $categories_result = db_query('SELECT c.cid, c.title, ci.iid FROM {aggregator_category} c LEFT JOIN {aggregator_category_item} ci ON c.cid = ci.cid AND ci.iid = :iid', array(':iid' => $iid));
-      $selected = array();
-      foreach ($categories_result as $category) {
-        if (!$done) {
-          $categories[$category->cid] = check_plain($category->title);
-        }
-        if ($category->iid) {
-          $selected[] = $category->cid;
-        }
-      }
-      $done = TRUE;
-      $form['items'][$iid]['item'] = $form_items[$iid];
-      $form['items'][$iid]['categories'] = array(
-        '#type' => config('aggregator.settings')->get('source.category_selector'),
-        '#default_value' => $selected,
-        '#options' => $categories,
-        '#size' => 10,
-        '#multiple' => TRUE,
-        '#parents' => array('categories', $iid),
-      );
-    }
-  }
-
-  $form['actions'] = array('#type' => 'actions');
-  $form['actions']['submit'] = array('#type' => 'submit', '#value' => t('Save categories'));
-  $form['pager'] = array('#theme' => 'pager');
-
-  return $form;
-}
-
-/**
- * Form submission handler for aggregator_categorize_items().
- */
-function aggregator_categorize_items_submit($form, &$form_state) {
-  if (!empty($form_state['values']['categories'])) {
-    foreach ($form_state['values']['categories'] as $iid => $selection) {
-      db_delete('aggregator_category_item')
-        ->condition('iid', $iid)
-        ->execute();
-      $insert = db_insert('aggregator_category_item')->fields(array('iid', 'cid'));
-      $has_values = FALSE;
-      foreach ($selection as $cid) {
-        if ($cid && $iid) {
-          $has_values = TRUE;
-          $insert->values(array(
-            'iid' => $iid,
-            'cid' => $cid,
-          ));
-        }
-      }
-      if ($has_values) {
-        $insert->execute();
-      }
-    }
+  $build['feed_source'] = is_array($feed_source) ? $feed_source : array('#markup' => $feed_source);
+  if ($items) {
+    $build['items'] = entity_view_multiple($items, 'default');
+    $build['pager'] = array('#theme' => 'pager');
   }
-  drupal_set_message(t('The categories have been saved.'));
+  return $build;
 }
 
 /**
diff --git a/core/modules/aggregator/aggregator.routing.yml b/core/modules/aggregator/aggregator.routing.yml
index 2c69045..76f534e 100644
--- a/core/modules/aggregator/aggregator.routing.yml
+++ b/core/modules/aggregator/aggregator.routing.yml
@@ -67,3 +67,18 @@ aggregator_categories:
     _content: '\Drupal\aggregator\Controller\AggregatorController::categories'
   requirements:
     _access_aggregator_categories: 'TRUE'
+
+aggregator_categorize_category_form:
+  pattern: '/aggregator/categories/{cid}/categorize'
+  defaults:
+    _form: '\Drupal\aggregator\Form\CategorizeCategoryForm'
+  requirements:
+    _permission: 'administer news feeds'
+
+aggregator_categorize_feed_form:
+  pattern: '/aggregator/sources/{aggregator_feed}/categorize'
+  defaults:
+    _form: '\Drupal\aggregator\Form\CategorizeFeedForm'
+    entity_type: 'aggregator_feed'
+  requirements:
+    _permission: 'administer news feeds'
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeCategoryForm.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeCategoryForm.php
new file mode 100644
index 0000000..4bc7c9e
--- /dev/null
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeCategoryForm.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\aggregator\Form\CategorizeCategoryForm
+ */
+
+namespace Drupal\aggregator\Form;
+
+/**
+ * A form for categorizing feed items in a feed category.
+ */
+class CategorizeCategoryForm extends CategorizeFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormID() {
+    return 'aggregator_page_category_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, array &$form_state, $cid = NULL) {
+    $items = $this->storageController->loadByCategory($cid);
+    return $this->prepareFormItems($items);
+  }
+
+}
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFeedForm.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFeedForm.php
new file mode 100644
index 0000000..6f29b60
--- /dev/null
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFeedForm.php
@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\aggregator\Form\CategorizeFeedForm
+ */
+
+namespace Drupal\aggregator\Form;
+
+use Drupal\aggregator\FeedInterface;
+
+/**
+ * A form for categorizing feed items from a feed.
+ */
+class CategorizeFeedForm extends CategorizeFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormID() {
+    return 'aggregator_page_source_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, array &$form_state, FeedInterface $aggregator_feed = NULL) {
+    $items = $this->storageController->loadByFeed($aggregator_feed->id());
+    return $this->prepareFormItems($items, $aggregator_feed);
+  }
+
+}
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFormBase.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFormBase.php
new file mode 100644
index 0000000..59fe4a0
--- /dev/null
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/CategorizeFormBase.php
@@ -0,0 +1,179 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\aggregator\Form\CategorizeFormBase.
+ */
+
+namespace Drupal\aggregator\Form;
+
+use Drupal\aggregator\ItemInterface;
+use Drupal\aggregator\ItemStorageControllerInterface;
+use Drupal\Component\Utility\String;
+use Drupal\Core\Config\Config;
+use Drupal\Core\Controller\ControllerInterface;
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityRenderControllerInterface;
+use Drupal\Core\Form\FormInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a base form to allow items to be categorized.
+ */
+abstract class CategorizeFormBase implements FormInterface, ControllerInterface {
+
+  /**
+   * The Render controller.
+   *
+   * @var \Drupal\Core\Entity\EntityRenderControllerInterface
+   */
+  protected $renderController;
+
+  /**
+   * The aggregator config.
+   *
+   * @var \Drupal\Core\Config\Config
+   */
+  protected $config;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection;
+   */
+  protected $database;
+
+  /**
+   * The aggregator item storage controller.
+   *
+   * @var \Drupal\aggregator\ItemStorageControllerInterface
+   */
+  protected $storageController;
+
+  /**
+   * Constructs a \Drupal\aggregator\Controller\AggregatorController object.
+   *
+   * @param \Drupal\Core\Entity\EntityRenderControllerInterface $render_controller
+   *   The item render controller.
+   * @param \Drupal\Core\Database\Connection $database
+   *   The database connection.
+   * @param \Drupal\Core\Config\Config $config
+   *   The aggregator config.
+   * @param \Drupal\aggregator\ItemStorageControllerInterface $storage_controller
+   *   The aggregator item storage controller.
+   */
+  public function __construct(EntityRenderControllerInterface $render_controller, Connection $database, Config $config, ItemStorageControllerInterface $storage_controller) {
+    $this->renderController = $render_controller;
+    $this->database = $database;
+    $this->config = $config;
+    $this->storageController = $storage_controller;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.entity')->getRenderController('aggregator_item'),
+      $container->get('database'),
+      $container->get('config.factory')->get('aggregator.settings'),
+      $container->get('plugin.manager.entity')->getStorageController('aggregator_item')
+    );
+  }
+
+  /**
+   * Prepares a list of items to be displayed in a form.
+   *
+   * @param \Drupal\aggregator\ItemInterface[] $items
+   *   An array of items.
+   * @param \Drupal\aggregator\FeedInterface|null $feed
+   *   (optional) The feed we are displaying.
+   *
+   * @return array
+   *   A form builder array.
+   */
+  protected function prepareFormItems($items, $feed = NULL) {
+
+    $form['feed_source'] = array(
+      '#value' => $feed,
+    );
+    $categories = array();
+    $done = FALSE;
+
+    $form['items'] = array(
+      '#type' => 'table',
+      '#header' => array('', t('Categorize')),
+    );
+    if ($items && ($form_items = $this->renderController->viewMultiple($items, 'default'))) {
+      foreach (element_children($form_items) as $iid) {
+        $categories_result = $this->database->query('SELECT c.cid, c.title, ci.iid FROM {aggregator_category} c LEFT JOIN {aggregator_category_item} ci ON c.cid = ci.cid AND ci.iid = :iid', array(':iid' => $iid));
+
+        $selected = array();
+        foreach ($categories_result as $category) {
+          if (!$done) {
+            $categories[$category->cid] = String::checkPlain($category->title);
+          }
+          if ($category->iid) {
+            $selected[] = $category->cid;
+          }
+        }
+        $done = TRUE;
+        $form['items'][$iid]['item'] = $form_items[$iid];
+        $form['items'][$iid]['categories'] = array(
+          '#type' => $this->config->get('source.category_selector'),
+          '#default_value' => $selected,
+          '#options' => $categories,
+          '#size' => 10,
+          '#multiple' => TRUE,
+          '#parents' => array('categories', $iid),
+        );
+      }
+    }
+
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['submit'] = array(
+      '#type' => 'submit',
+      '#value' => t('Save categories'),
+    );
+    $form['pager'] = array('#theme' => 'pager');
+
+    return $form;
+  }
+
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, array &$form_state) {
+    if (!empty($form_state['values']['categories'])) {
+      foreach ($form_state['values']['categories'] as $iid => $selection) {
+        $this->database->delete('aggregator_category_item')
+          ->condition('iid', $iid)
+          ->execute();
+        $insert = $this->database->insert('aggregator_category_item')
+          ->fields(array('iid', 'cid'));
+        $has_values = FALSE;
+        foreach ($selection as $cid) {
+          if ($cid && $iid) {
+            $has_values = TRUE;
+            $insert->values(array(
+              'iid' => $iid,
+              'cid' => $cid,
+            ));
+          }
+        }
+        if ($has_values) {
+          $insert->execute();
+        }
+      }
+    }
+    drupal_set_message(t('The categories have been saved.'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, array &$form_state) {
+  }
+
+}