diff --git a/extensions/tags/bootstrap.php b/extensions/tags/bootstrap.php
index bcde602ce..19039db79 100644
--- a/extensions/tags/bootstrap.php
+++ b/extensions/tags/bootstrap.php
@@ -1,5 +1,9 @@
 <?php
 
+// Require the extension's composer autoload file. This will enable all of our
+// classes in the src directory to be autoloaded.
 require 'vendor/autoload.php';
 
-$this->app->register('Flarum\Categories\CategoriesServiceProvider');
+// Register our service provider with the Flarum application. In here we can
+// register bindings and execute code when the application boots.
+$app->register('Flarum\Categories\CategoriesServiceProvider');
diff --git a/extensions/tags/js/bootstrap.js b/extensions/tags/js/bootstrap.js
index 00de45748..7eeeb273e 100644
--- a/extensions/tags/js/bootstrap.js
+++ b/extensions/tags/js/bootstrap.js
@@ -16,6 +16,7 @@ import icon from 'flarum/helpers/icon';
 import CategoriesPage from 'categories/components/categories-page';
 import Category from 'categories/category';
 import PostDiscussionMoved from 'categories/components/post-discussion-moved';
+import NotificationDiscussionMoved from 'categories/components/notification-discussion-moved';
 
 import app from 'flarum/app';
 
@@ -31,6 +32,7 @@ app.initializers.add('categories', function() {
   // app.routes['category.filter'] = ['/c/:slug/:filter', IndexPage.component({category: true})];
 
   app.postComponentRegistry['discussionMoved'] = PostDiscussionMoved;
+  app.notificationComponentRegistry['discussionMoved'] = NotificationDiscussionMoved;
   app.store.model('categories', Category);
 
   extend(DiscussionList.prototype, 'infoItems', function(items, discussion) {
diff --git a/extensions/tags/js/src/components/notification-discussion-moved.js b/extensions/tags/js/src/components/notification-discussion-moved.js
new file mode 100644
index 000000000..f3ef00481
--- /dev/null
+++ b/extensions/tags/js/src/components/notification-discussion-moved.js
@@ -0,0 +1,27 @@
+import Notification from 'flarum/components/notification';
+import avatar from 'flarum/helpers/avatar';
+import icon from 'flarum/helpers/icon';
+import username from 'flarum/helpers/username';
+import humanTime from 'flarum/helpers/human-time';
+
+export default class NotificationDiscussionMoved extends Notification {
+  content() {
+    var notification = this.props.notification;
+    var discussion = notification.subject();
+    var category = discussion.category();
+
+    return m('a', {href: app.route('discussion.near', {
+      id: discussion.id(),
+      slug: discussion.slug(),
+      near: notification.content().postNumber
+    }), config: m.route}, [
+      avatar(notification.sender()),
+      m('h3.notification-title', discussion.title()),
+      m('div.notification-info', [
+        icon('arrow-right'),
+        ' Moved to ', m('span.category', {style: 'color: '+category.color()}, category.title()), ' by ', username(notification.sender()),
+        ' ', humanTime(notification.time())
+      ])
+    ]);
+  }
+}
diff --git a/extensions/tags/src/Handlers/Handler.php b/extensions/tags/src/CategoriesHandler.php
similarity index 54%
rename from extensions/tags/src/Handlers/Handler.php
rename to extensions/tags/src/CategoriesHandler.php
index fae68dd60..c21b49753 100755
--- a/extensions/tags/src/Handlers/Handler.php
+++ b/extensions/tags/src/CategoriesHandler.php
@@ -1,35 +1,27 @@
-<?php namespace Flarum\Categories\Handlers;
+<?php namespace Flarum\Categories;
 
-use Flarum\Api\Events\SerializeRelationship;
-use Flarum\Api\Serializers\DiscussionSerializer;
-use Flarum\Support\Actor;
-use Flarum\Forum\Events\RenderView;
+use Flarum\Categories\Events\DiscussionWasMoved;
 use Flarum\Core\Events\ModelCall;
 use Flarum\Core\Events\RegisterDiscussionGambits;
-use Flarum\Core\Models\Discussion;
-use Flarum\Categories\Category;
-use Flarum\Categories\CategorySerializer;
-use Flarum\Categories\DiscussionMovedPost;
 use Flarum\Core\Events\DiscussionWillBeSaved;
+use Flarum\Core\Models\Discussion;
+use Flarum\Api\Events\SerializeRelationship;
+use Flarum\Api\Serializers\DiscussionSerializer;
+use Flarum\Forum\Events\RenderView;
 
-class Handler
+class CategoriesHandler
 {
-    public function __construct(Actor $actor)
-    {
-        $this->actor = $actor;
-    }
-
     public function subscribe($events)
     {
         $events->listen('Flarum\Forum\Events\RenderView', __CLASS__.'@renderForum');
         $events->listen('Flarum\Api\Events\SerializeRelationship', __CLASS__.'@serializeRelationship');
-        $events->listen('Flarum\Core\Events\RegisterDiscussionGambits', __CLASS__.'@registerGambits');
-        $events->listen('Flarum\Core\Events\DiscussionWillBeSaved', __CLASS__.'@saveCategoryToDiscussion');
+        $events->listen('Flarum\Core\Events\RegisterDiscussionGambits', __CLASS__.'@registerDiscussionGambits');
+        $events->listen('Flarum\Core\Events\DiscussionWillBeSaved', __CLASS__.'@whenDiscussionWillBeSaved');
     }
 
     public function renderForum(RenderView $event)
     {
-        $root = __DIR__.'/../..';
+        $root = __DIR__.'/..';
 
         $event->assets->addFile([
             $root.'/js/dist/extension.js',
@@ -40,7 +32,7 @@ class Handler
         $event->view->data = array_merge($event->view->data, $serializer->collection(Category::orderBy('position')->get())->toArray());
     }
 
-    public function saveCategoryToDiscussion(DiscussionWillBeSaved $event)
+    public function whenDiscussionWillBeSaved(DiscussionWillBeSaved $event)
     {
         if (isset($event->command->data['links']['category']['linkage'])) {
             $linkage = $event->command->data['links']['category']['linkage'];
@@ -56,37 +48,11 @@ class Handler
             }
 
             $discussion->category_id = $categoryId;
-
-            if ($discussion->exists) {
-                $lastPost = $discussion->posts()->orderBy('time', 'desc')->first();
-                if ($lastPost instanceof DiscussionMovedPost) {
-                    if ($lastPost->content[0] == $categoryId) {
-                        $lastPost->delete();
-                        $discussion->postWasRemoved($lastPost);
-                    } else {
-                        $newContent = $lastPost->content;
-                        $newContent[1] = $categoryId;
-                        $lastPost->content = $newContent;
-                        $lastPost->save();
-                        $discussion->postWasAdded($lastPost);
-                    }
-                } else {
-                    $post = DiscussionMovedPost::reply(
-                        $discussion->id,
-                        $user->id,
-                        $oldCategoryId,
-                        $categoryId
-                    );
-
-                    $post->save();
-
-                    $discussion->postWasAdded($post);
-                }
-            }
+            $discussion->raise(new DiscussionWasMoved($discussion, $user, $oldCategoryId));
         }
     }
 
-    public function registerGambits(RegisterDiscussionGambits $event)
+    public function registerDiscussionGambits(RegisterDiscussionGambits $event)
     {
         $event->gambits->add('Flarum\Categories\CategoryGambit');
     }
diff --git a/extensions/tags/src/CategoriesServiceProvider.php b/extensions/tags/src/CategoriesServiceProvider.php
index bd99b994a..6ce82ce4a 100644
--- a/extensions/tags/src/CategoriesServiceProvider.php
+++ b/extensions/tags/src/CategoriesServiceProvider.php
@@ -2,10 +2,11 @@
 
 use Illuminate\Support\ServiceProvider;
 use Illuminate\Contracts\Events\Dispatcher;
-use Flarum\Api\Actions\Discussions\IndexAction;
-use Flarum\Api\Actions\Discussions\ShowAction;
 use Flarum\Core\Models\Post;
 use Flarum\Core\Models\Discussion;
+use Flarum\Core\Notifications\Notifier;
+use Flarum\Api\Actions\Discussions\IndexAction as DiscussionsIndexAction;
+use Flarum\Api\Actions\Discussions\ShowAction as DiscussionsShowAction;
 
 class CategoriesServiceProvider extends ServiceProvider
 {
@@ -14,23 +15,31 @@ class CategoriesServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot(Dispatcher $events)
+    public function boot(Dispatcher $events, Notifier $notifier)
     {
-        $events->subscribe('Flarum\Categories\Handlers\Handler');
-
-        IndexAction::$include['category'] = true;
-
-        ShowAction::$include['category'] = true;
-
-        Post::addType('discussionMoved', 'Flarum\Categories\DiscussionMovedPost');
+        $events->subscribe('Flarum\Categories\CategoriesHandler');
+        $events->subscribe('Flarum\Categories\DiscussionMovedNotifier');
 
+        // Add the category relationship to the Discussion model, and include
+        // it in discussion-related API actions by default.
         Discussion::addRelationship('category', function ($model) {
             return $model->belongsTo('Flarum\Categories\Category', null, null, 'category');
         });
+        DiscussionsIndexAction::$include['category'] = true;
+        DiscussionsShowAction::$include['category'] = true;
+
+        // Add a new post and notification type to represent a discussion
+        // being moved from one category to another.
+        Post::addType('Flarum\Categories\DiscussionMovedPost');
+
+        $notifier->registerType('Flarum\Categories\DiscussionMovedNotification', ['alert' => true]);
     }
 
     public function register()
     {
-        //
+        $this->app->bind(
+            'Flarum\Categories\CategoryRepositoryInterface',
+            'Flarum\Categories\EloquentCategoryRepository'
+        );
     }
 }
diff --git a/extensions/tags/src/CategoryGambit.php b/extensions/tags/src/CategoryGambit.php
index 928a8bb9d..38b75ddcf 100644
--- a/extensions/tags/src/CategoryGambit.php
+++ b/extensions/tags/src/CategoryGambit.php
@@ -8,17 +8,39 @@ class CategoryGambit extends GambitAbstract
 {
     /**
      * The gambit's regex pattern.
+     *
      * @var string
      */
     protected $pattern = 'category:(.+)';
 
+    /**
+     * @var \Flarum\Categories\CategoryRepositoryInterface
+     */
+    protected $categories;
+
+    /**
+     * Instantiate the gambit.
+     *
+     * @param \Flarum\Categories\CategoryRepositoryInterface $categories
+     */
+    public function __construct(CategoryRepositoryInterface $categories)
+    {
+        $this->categories = $categories;
+    }
+
+    /**
+     * Apply conditions to the searcher, given matches from the gambit's
+     * regex.
+     *
+     * @param array $matches The matches from the gambit's regex.
+     * @param \Flarum\Core\Search\SearcherInterface $searcher
+     * @return void
+     */
     public function conditions($matches, SearcherInterface $searcher)
     {
         $slug = trim($matches[1], '"');
 
-        // @todo implement categories repository
-        // $id = $this->categories->getIdForSlug($slug);
-        $id = Category::whereSlug($slug)->pluck('id');
+        $id = $this->categories->getIdForSlug($slug);
 
         $searcher->query()->where('category_id', $id);
     }
diff --git a/extensions/tags/src/CategoryRepositoryInterface.php b/extensions/tags/src/CategoryRepositoryInterface.php
new file mode 100644
index 000000000..01c0875a9
--- /dev/null
+++ b/extensions/tags/src/CategoryRepositoryInterface.php
@@ -0,0 +1,24 @@
+<?php namespace Flarum\Categories;
+
+use Flarum\Core\Models\User;
+
+interface CategoryRepositoryInterface
+{
+    /**
+     * Find all categories, optionally making sure they are visible to a
+     * certain user.
+     *
+     * @param  \Flarum\Core\Models\User|null  $user
+     * @return \Illuminate\Database\Eloquent\Collection
+     */
+    public function find(User $user = null);
+
+    /**
+     * Get the ID of a category with the given slug.
+     *
+     * @param string $slug
+     * @param \Flarum\Core\Models\User|null $user
+     * @return integer
+     */
+    public function getIdForSlug($slug, User $user = null);
+}
diff --git a/extensions/tags/src/CategorySerializer.php b/extensions/tags/src/CategorySerializer.php
index 48ee398e4..367e1920f 100644
--- a/extensions/tags/src/CategorySerializer.php
+++ b/extensions/tags/src/CategorySerializer.php
@@ -11,6 +11,12 @@ class CategorySerializer extends BaseSerializer
      */
     protected $type = 'categories';
 
+    /**
+     * Serialize category attributes to be exposed in the API.
+     *
+     * @param \Flarum\Categories\Category $category
+     * @return array
+     */
     protected function attributes($category)
     {
         $attributes = [
diff --git a/extensions/tags/src/DiscussionMovedNotification.php b/extensions/tags/src/DiscussionMovedNotification.php
new file mode 100644
index 000000000..5c11cff6f
--- /dev/null
+++ b/extensions/tags/src/DiscussionMovedNotification.php
@@ -0,0 +1,39 @@
+<?php namespace Flarum\Categories;
+
+use Flarum\Core\Models\User;
+use Flarum\Core\Notifications\Types\Notification;
+use Flarum\Core\Notifications\Types\AlertableNotification;
+
+class DiscussionMovedNotification extends Notification implements AlertableNotification
+{
+    public $post;
+
+    public function __construct(User $recipient, User $sender, DiscussionMovedPost $post)
+    {
+        $this->post = $post;
+
+        parent::__construct($recipient, $sender);
+    }
+
+    public function getSubject()
+    {
+        return $this->post->discussion;
+    }
+
+    public function getAlertData()
+    {
+        return [
+            'postNumber' => $this->post->number
+        ];
+    }
+
+    public static function getType()
+    {
+        return 'discussionMoved';
+    }
+
+    public static function getSubjectModel()
+    {
+        return 'Flarum\Core\Models\Discussion';
+    }
+}
diff --git a/extensions/tags/src/DiscussionMovedNotifier.php b/extensions/tags/src/DiscussionMovedNotifier.php
new file mode 100755
index 000000000..71adacb55
--- /dev/null
+++ b/extensions/tags/src/DiscussionMovedNotifier.php
@@ -0,0 +1,58 @@
+<?php namespace Flarum\Categories;
+
+use Flarum\Categories\Events\DiscussionWasMoved;
+use Flarum\Core\Notifications\Notifier;
+use Illuminate\Contracts\Events\Dispatcher;
+
+class DiscussionMovedNotifier
+{
+    protected $notifier;
+
+    public function __construct(Notifier $notifier)
+    {
+        $this->notifier = $notifier;
+    }
+
+    /**
+     * Register the listeners for the subscriber.
+     *
+     * @param \Illuminate\Contracts\Events\Dispatcher $events
+     */
+    public function subscribe(Dispatcher $events)
+    {
+        $events->listen('Flarum\Categories\Events\DiscussionWasMoved', __CLASS__.'@whenDiscussionWasMoved');
+    }
+
+    public function whenDiscussionWasMoved(DiscussionWasMoved $event)
+    {
+        $post = $this->createPost($event);
+
+        $post = $event->discussion->addPost($post);
+
+        if ($event->discussion->start_user_id !== $event->user->id) {
+            $this->sendNotification($event, $post);
+        }
+    }
+
+    protected function createPost(DiscussionWasMoved $event)
+    {
+        return DiscussionMovedPost::reply(
+            $event->discussion->id,
+            $event->user->id,
+            $event->oldCategoryId,
+            $event->discussion->category_id
+        );
+    }
+
+    protected function sendNotification(DiscussionWasMoved $event, DiscussionMovedPost $post)
+    {
+        $notification = new DiscussionMovedNotification(
+            $event->discussion->startUser,
+            $event->user,
+            $post,
+            $event->discussion->category_id
+        );
+
+        $this->notifier->send($notification);
+    }
+}
diff --git a/extensions/tags/src/DiscussionMovedPost.php b/extensions/tags/src/DiscussionMovedPost.php
index a5cd59639..a1287f3c0 100755
--- a/extensions/tags/src/DiscussionMovedPost.php
+++ b/extensions/tags/src/DiscussionMovedPost.php
@@ -1,49 +1,63 @@
 <?php namespace Flarum\Categories;
 
-use Flarum\Core\Models\Post;
+use Flarum\Core\Models\Model;
+use Flarum\Core\Models\ActivityPost;
 
-class DiscussionMovedPost extends Post
+class DiscussionMovedPost extends ActivityPost
 {
+    /**
+     * The type of post this is, to be stored in the posts table.
+     *
+     * @var string
+     */
+    public static $type = 'discussionMoved';
+
+    /**
+     * Merge the post into another post of the same type.
+     *
+     * @param \Flarum\Core\Models\Model $previous
+     * @return boolean true if the post was merged, false if it was deleted.
+     */
+    protected function mergeInto(Model $previous)
+    {
+        if ($previous->content[0] == $this->content[1]) {
+            return false;
+        }
+
+        $previous->content = static::buildContent($previous->content[0], $this->content[1]);
+        return true;
+    }
+
     /**
      * Create a new instance in reply to a discussion.
      *
-     * @param  int  $discussionId
-     * @param  int  $userId
-     * @param  string  $oldTitle
-     * @param  string  $newTitle
+     * @param integer $discussionId
+     * @param integer $userId
+     * @param integer $oldCategoryId
+     * @param integer $newCategoryId
      * @return static
      */
     public static function reply($discussionId, $userId, $oldCategoryId, $newCategoryId)
     {
         $post = new static;
 
-        $post->content       = [$oldCategoryId, $newCategoryId];
+        $post->content       = static::buildContent($oldCategoryId, $newCategoryId);
         $post->time          = time();
         $post->discussion_id = $discussionId;
         $post->user_id       = $userId;
-        $post->type          = 'discussionMoved';
 
         return $post;
     }
 
     /**
-     * Unserialize the content attribute.
+     * Build the content attribute.
      *
-     * @param  string  $value
-     * @return string
+     * @param boolean $oldCategoryId The old category ID.
+     * @param boolean $newCategoryId The new category ID.
+     * @return array
      */
-    public function getContentAttribute($value)
+    public static function buildContent($oldCategoryId, $newCategoryId)
     {
-        return json_decode($value);
-    }
-
-    /**
-     * Serialize the content attribute.
-     *
-     * @param  string  $value
-     */
-    public function setContentAttribute($value)
-    {
-        $this->attributes['content'] = json_encode($value);
+        return [$oldCategoryId, $newCategoryId];
     }
 }
diff --git a/extensions/tags/src/EloquentCategoryRepository.php b/extensions/tags/src/EloquentCategoryRepository.php
new file mode 100644
index 000000000..a04a2408e
--- /dev/null
+++ b/extensions/tags/src/EloquentCategoryRepository.php
@@ -0,0 +1,52 @@
+<?php namespace Flarum\Categories;
+
+use Illuminate\Database\Eloquent\Builder;
+use Flarum\Core\Models\User;
+use Flarum\Categories\Category;
+
+class EloquentCategoryRepository implements CategoryRepositoryInterface
+{
+    /**
+     * Find all categories, optionally making sure they are visible to a
+     * certain user.
+     *
+     * @param  \Flarum\Core\Models\User|null  $user
+     * @return \Illuminate\Database\Eloquent\Collection
+     */
+    public function find(User $user = null)
+    {
+        $query = Category::newQuery();
+
+        return $this->scopeVisibleForUser($query, $user)->get();
+    }
+
+    /**
+     * Get the ID of a category with the given slug.
+     *
+     * @param string $slug
+     * @param \Flarum\Core\Models\User|null $user
+     * @return integer
+     */
+    public function getIdForSlug($slug, User $user = null)
+    {
+        $query = Category::where('slug', 'like', $slug);
+
+        return $this->scopeVisibleForUser($query, $user)->pluck('id');
+    }
+
+    /**
+     * Scope a query to only include records that are visible to a user.
+     *
+     * @param  \Illuminate\Database\Eloquent\Builder  $query
+     * @param  \Flarum\Core\Models\User  $user
+     * @return \Illuminate\Database\Eloquent\Builder
+     */
+    protected function scopeVisibleForUser(Builder $query, User $user = null)
+    {
+        if ($user !== null) {
+            $query->whereCan($user, 'view');
+        }
+
+        return $query;
+    }
+}
diff --git a/extensions/tags/src/Events/DiscussionWasMoved.php b/extensions/tags/src/Events/DiscussionWasMoved.php
new file mode 100644
index 000000000..6393accbe
--- /dev/null
+++ b/extensions/tags/src/Events/DiscussionWasMoved.php
@@ -0,0 +1,34 @@
+<?php namespace Flarum\Categories\Events;
+
+use Flarum\Core\Models\Discussion;
+use Flarum\Core\Models\User;
+
+class DiscussionWasMoved
+{
+    /**
+     * @var \Flarum\Core\Models\Discussion
+     */
+    public $discussion;
+
+    /**
+     * @var \Flarum\Core\Models\User
+     */
+    public $user;
+
+    /**
+     * @var integer
+     */
+    public $oldCategoryId;
+
+    /**
+     * @param \Flarum\Core\Models\Discussion $discussion
+     * @param \Flarum\Core\Models\User $user
+     * @param \Flarum\Categories\Category $oldCategory
+     */
+    public function __construct(Discussion $discussion, User $user, $oldCategoryId)
+    {
+        $this->discussion = $discussion;
+        $this->user = $user;
+        $this->oldCategoryId = $oldCategoryId;
+    }
+}