diff --git a/src/app/Models/User.php b/src/app/Models/User.php
index 741315d8..62c8754c 100644
--- a/src/app/Models/User.php
+++ b/src/app/Models/User.php
@@ -2,6 +2,7 @@
 
 namespace App\Models;
 
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Foundation\Auth\User as Authenticatable;
 use Laravel\Sanctum\HasApiTokens;
 
@@ -33,4 +34,14 @@ protected function casts(): array
             'email_verified_at'       => 'datetime',
         ];
     }
+
+    public function favorites(): BelongsToMany
+    {
+        return $this->belongsToMany(
+            WorldHeritage::class,
+            'user_favorite',
+            'user_id',
+            'world_heritage_site_id'
+        );
+    }
 }
\ No newline at end of file
diff --git a/src/app/Packages/Domains/Favorite/FavoriteRepository.php b/src/app/Packages/Domains/Favorite/FavoriteRepository.php
new file mode 100644
index 00000000..6fa2205d
--- /dev/null
+++ b/src/app/Packages/Domains/Favorite/FavoriteRepository.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Packages\Domains\Favorite;
+
+use App\Models\User;
+use App\Packages\Domains\Favorite\Interface\FavoriteRepositoryInterface;
+use Exception;
+
+class FavoriteRepository implements FavoriteRepositoryInterface
+{
+    public function __construct(
+        private User $userModel
+    ) {}
+
+    public function addFavorite(int $userId, int $worldHeritageSiteId): void
+    {
+        $user = $this->userModel->find($userId);
+
+        if ($user === null) {
+            throw new Exception('User not found.');
+        }
+
+        $user->favorites()->attach($worldHeritageSiteId);
+    }
+}
diff --git a/src/app/Packages/Domains/Favorite/Interface/FavoriteRepositoryInterface.php b/src/app/Packages/Domains/Favorite/Interface/FavoriteRepositoryInterface.php
new file mode 100644
index 00000000..7b1291ac
--- /dev/null
+++ b/src/app/Packages/Domains/Favorite/Interface/FavoriteRepositoryInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace App\Packages\Domains\Favorite\Interface;
+
+interface FavoriteRepositoryInterface
+{
+    public function addFavorite(int $userId, int $worldHeritageSiteId): void;
+}
diff --git a/src/app/Packages/Domains/Favorite/Tests/FavoriteRepositoryTest.php b/src/app/Packages/Domains/Favorite/Tests/FavoriteRepositoryTest.php
new file mode 100644
index 00000000..7b71a092
--- /dev/null
+++ b/src/app/Packages/Domains/Favorite/Tests/FavoriteRepositoryTest.php
@@ -0,0 +1,93 @@
+<?php
+
+namespace App\Packages\Domains\Favorite\Tests;
+
+use App\Models\User;
+use App\Models\WorldHeritage;
+use App\Packages\Domains\Favorite\FavoriteRepository;
+use Exception;
+use Faker\Factory as FakerFactory;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCase;
+
+class FavoriteRepositoryTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->truncate();
+    }
+
+    protected function tearDown(): void
+    {
+        $this->truncate();
+        parent::tearDown();
+    }
+
+    private function truncate(): void
+    {
+        if (env('APP_ENV') === 'testing') {
+            DB::connection('mysql')->statement('SET FOREIGN_KEY_CHECKS=0;');
+            DB::connection('mysql')->table('user_favorite')->truncate();
+            WorldHeritage::truncate();
+            User::truncate();
+            DB::connection('mysql')->statement('SET FOREIGN_KEY_CHECKS=1;');
+        }
+    }
+
+    private function repository(): FavoriteRepository
+    {
+        return new FavoriteRepository(new User());
+    }
+
+    private function seedUser(): User
+    {
+        $faker = FakerFactory::create();
+
+        return User::create([
+            'first_name'              => $faker->firstName(),
+            'last_name'               => $faker->lastName(),
+            'email'                   => $faker->unique()->safeEmail(),
+            'password'                => bcrypt('password'),
+            'age_range'               => 'teens',
+            'subscription_tier'       => 'free',
+            'subscription_expires_at' => null,
+        ]);
+    }
+
+    private function seedWorldHeritage(int $id): WorldHeritage
+    {
+        return WorldHeritage::create([
+            'id'             => $id,
+            'official_name'  => 'Example Site',
+            'name'           => 'Example Site',
+            'region'         => 'Asia',
+            'category'       => 'Cultural',
+            'criteria'       => ['i'],
+            'year_inscribed' => 2000,
+        ]);
+    }
+
+    public function test_addFavorite_attaches_world_heritage_site_to_user(): void
+    {
+        $user          = $this->seedUser();
+        $worldHeritage = $this->seedWorldHeritage(1);
+
+        $this->repository()->addFavorite($user->id, $worldHeritage->id);
+
+        $this->assertDatabaseHas('user_favorite', [
+            'user_id'                => $user->id,
+            'world_heritage_site_id' => $worldHeritage->id,
+        ]);
+    }
+
+    public function test_addFavorite_throws_exception_when_user_not_found(): void
+    {
+        $worldHeritage = $this->seedWorldHeritage(1);
+
+        $this->expectException(Exception::class);
+        $this->expectExceptionMessage('User not found.');
+
+        $this->repository()->addFavorite(999999, $worldHeritage->id);
+    }
+}
diff --git a/src/app/Providers/RepositoryProvider.php b/src/app/Providers/RepositoryProvider.php
index cbba05bf..50348344 100644
--- a/src/app/Providers/RepositoryProvider.php
+++ b/src/app/Providers/RepositoryProvider.php
@@ -2,6 +2,8 @@
 
 namespace App\Providers;
 
+use App\Packages\Domains\Favorite\FavoriteRepository;
+use App\Packages\Domains\Favorite\Interface\FavoriteRepositoryInterface;
 use App\Packages\Domains\User\Interface\UserRepositroyInterface;
 use App\Packages\Domains\User\UserRepository;
 use App\Packages\Domains\WorldHeritageRepository;
@@ -21,6 +23,11 @@ public function register(): void
             UserRepositroyInterface::class,
             UserRepository::class
         );
+
+        $this->app->bind(
+            FavoriteRepositoryInterface::class,
+            FavoriteRepository::class
+        );
     }
 
     public function boot(): void