diff --git a/src/ZammadClient.php b/src/ZammadClient.php
new file mode 100644
index 0000000..ff7fe5f
--- /dev/null
+++ b/src/ZammadClient.php
@@ -0,0 +1,183 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ZammadAPIClient;
+
+use GuzzleHttp\Client as GuzzleClient;
+use GuzzleHttp\Psr7\HttpFactory;
+use InvalidArgumentException;
+use ZammadAPIClient\Core\Contracts\ClientInterface;
+use ZammadAPIClient\Core\Contracts\DTOInterface;
+use ZammadAPIClient\Core\Contracts\RequestHandlerInterface;
+use ZammadAPIClient\Core\AbstractRepository;
+use ZammadAPIClient\Core\RepositoryRegistry;
+use ZammadAPIClient\Core\RequestHandler;
+use ZammadAPIClient\Core\RetryAfterMiddleware;
+
+final class ZammadClient implements ClientInterface
+{
+    public const USER_AGENT = 'Zammad API PHP';
+
+    /** @var array<class-string, object> */
+    private array $repos = [];
+
+    public function __construct(
+        private RequestHandlerInterface $handler,
+    ) {
+    }
+
+    /**
+     * Convenience factory with multiple authentication modes.
+     *
+     * Token auth (preferred):
+     *   ZammadClient::connect($url, token: 'your-token')
+     *
+     * OAuth2:
+     *   ZammadClient::connect($url, oauth2: 'your-token')
+     *
+     * Basic auth:
+     *   ZammadClient::connect($url, user: 'admin@example.com', pass: 'test')
+     *
+     * @param bool $debug      Enables Guzzle debug mode (request/response body to stdout).
+     * @param bool $verifySsl  false to disable TLS certificate verification.
+     */
+    public static function connect(
+        string $url,
+        ?string $token = null,
+        ?string $oauth2 = null,
+        ?string $user = null,
+        ?string $pass = null,
+        int $maxRetries = 3,
+        bool $debug = false,
+        bool $verifySsl = true,
+    ): self {
+        $headers = ['User-Agent' => self::USER_AGENT];
+
+        if ($token !== null && $token !== '' && $token !== '0') {
+            $headers['Authorization'] = "Token token={$token}";
+        } elseif ($oauth2 !== null && $oauth2 !== '' && $oauth2 !== '0') {
+            $headers['Authorization'] = "Bearer {$oauth2}";
+        } elseif ($user !== null && $pass !== null) {
+            $headers['Authorization'] = 'Basic ' . base64_encode("{$user}:{$pass}");
+        } else {
+            throw new InvalidArgumentException(
+                'Provide one of: token, oauth2, or user+pass for authentication.'
+            );
+        }
+
+        $http = new RetryAfterMiddleware(
+            new GuzzleClient([
+                'headers' => $headers,
+                'debug'   => $debug,
+                'verify'  => $verifySsl,
+            ]),
+            maxRetries: $maxRetries,
+        );
+
+        $factory = new HttpFactory();
+        $handler = new RequestHandler($http, $factory, $factory, $url);
+
+        return new self($handler);
+    }
+
+    /**
+     * Activates API-level impersonation for all subsequent requests.
+     *
+     * Forwards $userId as X-On-Behalf-Of header. The header stays active
+     * until unsetOnBehalfOfUser() is called.
+     */
+    public function setOnBehalfOfUser(?int $userId): void
+    {
+        $this->handler->setOnBehalfOfUser($userId);
+    }
+
+    public function unsetOnBehalfOfUser(): void
+    {
+        $this->handler->setOnBehalfOfUser(null);
+    }
+
+    /**
+     * Executes a closure with a temporary impersonation header.
+     *
+     * Ruby-style: client.perform_on_behalf_of(user_id) { ... }
+     * The header is set before the callback and cleared afterwards.
+     */
+    public function performOnBehalfOf(int $userId, callable $callback): mixed
+    {
+        $previous = null;
+
+        $this->handler->setOnBehalfOfUser($userId);
+
+        try {
+            return $callback($this);
+        } finally {
+            $this->handler->setOnBehalfOfUser(null);
+        }
+    }
+
+    /**
+     * Ruby-style resource accessor: $client->ticket()->find(1)
+     *
+     * Maps the method name to a repository using RepositoryRegistry
+     * via DTO class name lookup. Example:
+     *   ticket()    → TicketRepository
+     *   user()      → UserRepository
+     *   group()     → GroupRepository
+     *   ticket_article() → TicketArticleRepository
+     *
+     * @param array<array-key, mixed> $args
+     */
+    public function __call(string $name, array $args): AbstractRepository
+    {
+        $camel = implode('', array_map('ucfirst', explode('_', $name)));
+
+        foreach (RepositoryRegistry::DEFINITIONS as $repoClass => $def) {
+            $dtoShort = substr(strrchr($def['dto'], '\\') ?: '', 1);
+            $repoShort = substr(strrchr($repoClass, '\\') ?: '', 1);
+
+            if (
+                strcasecmp($dtoShort, $camel . 'DTO') === 0
+                || strcasecmp($repoShort, $camel . 'Repository') === 0
+                || strcasecmp($dtoShort, $camel) === 0
+            ) {
+                return $this->repo($repoClass);
+            }
+        }
+
+        throw new InvalidArgumentException("Unknown resource: {$name}");
+    }
+
+    /**
+     * Returns a memoized repository for the given repository class.
+     *
+     * @template T of AbstractRepository
+     * @param class-string<T> $repositoryClass
+     * @return T
+     */
+    public function repo(string $repositoryClass): AbstractRepository
+    {
+        $definition = RepositoryRegistry::definition($repositoryClass);
+
+        /** @var T */
+        return $this->repository($repositoryClass, $definition['path'], $definition['dto']);
+    }
+
+    /**
+     * @template T of AbstractRepository
+     * @param class-string<T>           $repoClass
+     * @param class-string<DTOInterface> $dtoClass
+     * @return T
+     */
+    private function repository(string $repoClass, string $path, string $dtoClass): object
+    {
+        if (!isset($this->repos[$repoClass])) {
+            $this->repos[$repoClass] = new $repoClass($this->handler, $path, $dtoClass);
+        }
+
+        /** @var T $repo */
+        $repo = $this->repos[$repoClass];
+
+        return $repo;
+    }
+}
diff --git a/test/Integration/TicketIntegrationTest.php b/test/Integration/TicketIntegrationTest.php
new file mode 100644
index 0000000..4966a26
--- /dev/null
+++ b/test/Integration/TicketIntegrationTest.php
@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ZammadAPIClient\Tests\Integration;
+
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\TestCase;
+use ZammadAPIClient\Endpoints\Tickets\TicketDTO;
+use ZammadAPIClient\Exceptions\NotFoundException;
+use ZammadAPIClient\ZammadClient;
+
+#[Group('integration')]
+final class TicketIntegrationTest extends TestCase
+{
+    private static ZammadClient $client;
+    private static array $createdIds = [];
+
+    public static function setUpBeforeClass(): void
+    {
+        $url   = getenv('ZAMMAD_URL') ?: null;
+        $token = getenv('ZAMMAD_TOKEN') ?: null;
+        $user  = getenv('ZAMMAD_USER') ?: null;
+        $pass  = getenv('ZAMMAD_PASS') ?: null;
+
+        if ($url === null || $url === '') {
+            self::markTestSkipped(
+                'Integration tests require ZAMMAD_URL environment variable. '
+                . 'Run: ZAMMAD_URL=http://127.0.0.1:8080/api/v1 ZAMMAD_TOKEN=xxx vendor/bin/phpunit --group=integration'
+            );
+        }
+
+        if ($token !== null && $token !== '') {
+            self::$client = ZammadClient::connect($url, token: $token);
+        } elseif ($user !== null && $pass !== null && $user !== '' && $pass !== '') {
+            self::$client = ZammadClient::connect($url, user: $user, pass: $pass);
+        } else {
+            self::markTestSkipped(
+                'Integration tests require ZAMMAD_TOKEN or ZAMMAD_USER+ZAMMAD_PASS environment variables. '
+                . 'Run: ZAMMAD_URL=http://127.0.0.1:8080/api/v1 ZAMMAD_TOKEN=xxx vendor/bin/phpunit --group=integration'
+            );
+        }
+    }
+
+    public function testCreateTicket(): void
+    {
+        $ticket = self::$client->ticket()->create(new TicketDTO(
+            id: null,
+            group_id: 1,
+            priority_id: 2,
+            state_id: 1,
+            organization_id: null,
+            customer_id: null,
+            owner_id: null,
+            title: 'Integration Test ' . uniqid('', true),
+            number: null,
+            created_at: null,
+            updated_at: null,
+        ));
+
+        self::assertGreaterThan(0, $ticket->id);
+        self::assertEquals(1, $ticket->group_id);
+        self::assertNotEmpty($ticket->title);
+
+        self::$createdIds[] = $ticket->id;
+    }
+
+    public function testFindTicket(): void
+    {
+        if (empty(self::$createdIds)) {
+            $this->markTestSkipped('No ticket created — run testCreateTicket first.');
+        }
+
+        $id = self::$createdIds[0];
+        $ticket = self::$client->ticket()->find($id);
+
+        self::assertEquals($id, $ticket->id);
+        self::assertNotEmpty($ticket->title);
+    }
+
+    public function testPatchTicket(): void
+    {
+        if (empty(self::$createdIds)) {
+            $this->markTestSkipped('No ticket created — run testCreateTicket first.');
+        }
+
+        $id = self::$createdIds[0];
+        $newTitle = 'Patched ' . uniqid('', true);
+
+        $patched = self::$client->ticket()->patch($id, ['title' => $newTitle]);
+        self::assertEquals($newTitle, $patched->title);
+    }
+
+    public function testDeleteTicket(): void
+    {
+        if (empty(self::$createdIds)) {
+            $this->markTestSkipped('No ticket created — run testCreateTicket first.');
+        }
+
+        $id = self::$createdIds[0];
+        self::$client->ticket()->delete($id);
+
+        $this->expectException(NotFoundException::class);
+        self::$client->ticket()->find($id);
+    }
+}
diff --git a/test/Unit/ZammadClientTest.php b/test/Unit/ZammadClientTest.php
new file mode 100644
index 0000000..b8829e5
--- /dev/null
+++ b/test/Unit/ZammadClientTest.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ZammadAPIClient\Tests\Unit;
+
+use Mockery;
+use Mockery\Adapter\Phpunit\MockeryTestCase;
+use PHPUnit\Framework\Attributes\Group;
+use ZammadAPIClient\Core\Contracts\RequestHandlerInterface;
+use ZammadAPIClient\Endpoints\Tickets\TicketRepository;
+use ZammadAPIClient\ZammadClient;
+
+#[Group('unit')]
+final class ZammadClientTest extends MockeryTestCase
+{
+    public function testRepoReturnsMemoizedRepositoryInstance(): void
+    {
+        $handler = Mockery::mock(RequestHandlerInterface::class);
+        $client = new ZammadClient($handler);
+
+        $first = $client->repo(TicketRepository::class);
+        $second = $client->repo(TicketRepository::class);
+
+        self::assertSame($first, $second);
+        self::assertInstanceOf(TicketRepository::class, $first);
+    }
+
+    public function testRepoThrowsForUnknownRepositoryClass(): void
+    {
+        $handler = Mockery::mock(RequestHandlerInterface::class);
+        $client = new ZammadClient($handler);
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Unknown repository');
+
+        $client->repo('NotARepository');
+    }
+}