diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 416571d..df061d2 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -155,10 +155,7 @@ function aggregator_menu() {
   $items['aggregator/categories/%aggregator_category'] = array(
     'title callback' => '_aggregator_category_title',
     'title arguments' => array(2),
-    'page callback' => 'aggregator_page_category',
-    'page arguments' => array(2),
-    'access arguments' => array('access news feeds'),
-    'file' => 'aggregator.pages.inc',
+    'route_name' => 'aggregator_page_category',
   );
   $items['aggregator/categories/%aggregator_category/view'] = array(
     'title' => 'View',
@@ -166,11 +163,8 @@ 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_page_category_form',
   );
   $items['aggregator/categories/%aggregator_category/configure'] = array(
     'title' => 'Configure',
@@ -242,6 +236,8 @@ function aggregator_menu() {
  *   A string with the aggregator category title.
  */
 function _aggregator_category_title($category) {
+  // @todo improve how the $category is handled, should be an object already
+  $category = aggregator_category_load($category);
   return $category->title;
 }
 
diff --git a/core/modules/aggregator/aggregator.pages.inc b/core/modules/aggregator/aggregator.pages.inc
index ca8ecad..69f3034 100644
--- a/core/modules/aggregator/aggregator.pages.inc
+++ b/core/modules/aggregator/aggregator.pages.inc
@@ -47,45 +47,6 @@ function aggregator_page_source_form($form, $form_state, $feed) {
 }
 
 /**
- * Form constructor to list items aggregated in a category.
- *
- * @param $category
- *   The category for which to list all of the aggregated items.
- *
- * @return string
- *   The rendered list of items for the feed.
- *
- * @see aggregator_menu()
- * @ingroup forms
- */
-function aggregator_page_category($category) {
-  drupal_add_feed('aggregator/rss/' . $category->cid, config('system.site')->get('name') . ' ' . t('aggregator - @title', array('@title' => $category->title)));
-
-  // It is safe to include the cid in the query because it's loaded from the
-  // database by aggregator_category_load().
-  $items = aggregator_load_feed_items('category', $category);
-
-  return _aggregator_page_list($items, arg(3));
-}
-
-/**
- * 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 $type
diff --git a/core/modules/aggregator/aggregator.routing.yml b/core/modules/aggregator/aggregator.routing.yml
index 2c69045..a9764c1 100644
--- a/core/modules/aggregator/aggregator.routing.yml
+++ b/core/modules/aggregator/aggregator.routing.yml
@@ -67,3 +67,17 @@ aggregator_categories:
     _content: '\Drupal\aggregator\Controller\AggregatorController::categories'
   requirements:
     _access_aggregator_categories: 'TRUE'
+
+aggregator_page_category:
+  pattern: '/aggregator/categories/{category}'
+  defaults:
+    _content: '\Drupal\aggregator\Controller\AggregatorController::pageCategory'
+  requirements:
+    _permission: 'access news feeds'
+
+aggregator_page_category_form:
+  pattern: '/aggregator/categories/{category}/categorize'
+  defaults:
+    _form: '\Drupal\aggregator\Form\AggregatorCategoryForm'
+  requirements:
+    _permission: 'administer news feeds'
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php b/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
index a8b1d80..bc2705f 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
@@ -265,8 +265,7 @@ public function categories() {
   public function pageLast() {
     drupal_add_feed('aggregator/rss', $this->configFactory->get('system.site')->get('name') . ' ' . t('aggregator'));
 
-    // @todo Refactor this function once after all controller conversions are
-    // done.
+    // @todo Refactor this once all controller conversions are complete.
     $this->moduleHandler->loadInclude('aggregator', 'inc', 'aggregator.pages');
     $items = aggregator_load_feed_items('sum');
 
@@ -323,4 +322,31 @@ public function sources() {
     return $build;
   }
 
+  /**
+   * Form constructor to list items aggregated in a category.
+   *
+   * @param $category
+   *   The category for which to list all of the aggregated items.
+   *
+   * @return string
+   *   The rendered list of items for the feed.
+   *
+   * @see aggregator_menu()
+   * @ingroup forms
+   */
+  public function pageCategory($category) {
+    // @todo Refactor this once all controller conversions are complete.
+    $this->moduleHandler->loadInclude('aggregator', 'inc', 'aggregator.pages');
+
+    // @todo improve how the $category is handled, should be an object already
+    $category = aggregator_category_load($category);
+
+    drupal_add_feed('aggregator/rss/' . $category->cid, config('system.site')->get('name') . ' ' . t('aggregator - @title', array('@title' => $category->title)));
+
+    // It is safe to include the cid in the query because it's loaded from the
+    // database by aggregator_category_load().
+    $items = aggregator_load_feed_items('category', $category);
+
+    return _aggregator_page_list($items, arg(3));
+  }
 }
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/AggregatorCategoryForm.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/AggregatorCategoryForm.php
new file mode 100644
index 0000000..51b66f7
--- /dev/null
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/AggregatorCategoryForm.php
@@ -0,0 +1,182 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\aggregator\Form\AggregatorCategoryForm.
+ */
+
+namespace Drupal\aggregator\Form;
+
+use Drupal\aggregator\Controller\AggregatorController;
+use Drupal\Component\Utility\String;
+use Drupal\Core\Config\ConfigFactory;
+use Drupal\Core\Controller\ControllerInterface;
+use Drupal\Core\Database\Connection;
+use Drupal\Core\Entity\EntityManager;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Form\FormInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form to allow items to be categorized.
+ */
+class AggregatorCategoryForm implements FormInterface, ControllerInterface {
+
+  /**
+   * Stores the Entity manager.
+   *
+   * @var \Drupal\Core\Entity\EntityManager
+   */
+  protected $entityManager;
+
+  /**
+   * Stores the Config Factory.
+   *
+   * @var \Drupal\Core\Config\ConfigFactory
+   */
+  protected $configFactory;
+
+  /**
+   * The database connection.
+   *
+   * @var \Drupal\Core\Database\Connection;
+   */
+  protected $database;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * Constructs a \Drupal\aggregator\Controller\AggregatorController object.
+   *
+   * @param \Drupal\Core\Entity\EntityManager $entity_manager
+   *   The Entity manager.
+   * @param \Drupal\Core\Config\ConfigFactory $config_factory
+   *   The config factory.
+   * @param \Drupal\Core\Database\Connection $database
+   *   The database connection.
+   * @param \Drupal\Core\Config\ConfigFactory $config_factory
+   *   The config factory.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   */
+  public function __construct(EntityManager $entity_manager, Connection $database, ConfigFactory $config_factory, ModuleHandlerInterface $module_handler) {
+    $this->entityManager = $entity_manager;
+    $this->database = $database;
+    $this->configFactory = $config_factory;
+    $this->moduleHandler = $module_handler;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.entity'),
+      $container->get('database'),
+      $container->get('config.factory'),
+      $container->get('module_handler')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormID() {
+    return 'aggregator_category_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, array &$form_state, $category = NULL) {
+    $this->moduleHandler->loadInclude('aggregator', 'inc', 'aggregator.pages');
+    // @todo Remove once categories are taxonomy terms - see
+    //   https://drupal.org/node/15266.
+    $category = aggregator_category_load($category);
+    // @todo Remove once aggregator_load_feed_items() is a method on the
+    //   \Drupal\aggregator\ItemStorageController, see
+    //   https://drupal.org/node/2043581
+    $items = aggregator_load_feed_items('category', $category);
+    $form['feed_source'] = array(
+      '#value' => '',
+    );
+    $categories = array();
+    $done = FALSE;
+
+    $form['items'] = array(
+      '#type' => 'table',
+      '#header' => array('', t('Categorize')),
+    );
+    if ($items && ($form_items = $this->entityManager->getRenderController('aggregator_item')->viewMultiple($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->configFactory->get('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 $form;  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, array &$form_state) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$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.'));
+  }
+
+}