diff --git a/README.md b/README.md
index c0eb7bb..ca4564a 100644
--- a/README.md
+++ b/README.md
@@ -25,7 +25,8 @@ Example:
 $keycloak = new \Fschmtt\Keycloak\Keycloak(
     baseUrl: 'http://keycloak:8080',
     username: 'admin',
-    password: 'admin'
+    password: 'admin',
+    realm: 'master'
 );
 
 $serverInfo = $keycloak->serverInfo()->get();
@@ -51,6 +52,8 @@ will print e.g.
 Keycloak 26.0.0 is running on Linux/5.10.25-linuxkit (amd64) with OpenJDK 64-Bit Server VM/11.0.11 since 0 days, 2 hours, 37 minutes, 7 seconds and is currently using 139 MB of 512 MB (28 %) memory.
 ```
 
+You can authenticate against a specific realm by passing it via the `realm` parameter when constructing the `Keycloak` instance.
+
 More examples can be found in the [examples](examples) directory.
 
 ## Customization
@@ -163,23 +166,27 @@ $myCustomRepresentation = $myCustomResource->myCustomEndpoint();
 
 ### [Users](https://www.keycloak.org/docs-api/26.0.0/rest-api/index.html#_users)
 
-| Endpoint                                                | Response                                                        | API                                                            |
-|---------------------------------------------------------|-----------------------------------------------------------------|----------------------------------------------------------------|
-| `GET /admin/realms/{realm}/users`                       | [UserCollection](src/Collection/UserCollection.php)             | [Users::all()](src/Resource/Users.php)                         |
-| `POST /admin/realms/{realm}/users`                      | `n/a`                                                           | [Users::create()](src/Resource/Users.php)                      |
-| `GET /admin/realms/{realm}/users/{userId}`              | [User](src/Representation/User.php)                             | [Users::get()](src/Resource/Users.php)                         |
-| `PUT /admin/realms/{realm}/users/{userId}`              | `n/a`                                                           | [Users::update()](src/Resource/Users.php)                      |
-| `DELETE /admin/realms/{realm}/users/{userId}`           | `n/a`                                                           | [Users::delete()](src/Resource/Users.php)                      |
-| `GET /admin/realms/{realm}/users`                       | [UserCollection](src/Collection/UserCollection.php)             | [Users::search()](src/Resource/Users.php)                      |
-| `PUT /{realm}/users/{id}/groups/{groupId}`              | `n/a`                                                           | [Users::joinGroup()](src/Resource/Users.php)                   |
-| `DELETE /{realm}/users/{id}/groups/{groupId}`           | `n/a`                                                           | [Users::leaveGroup()](src/Resource/Users.php)                  |
-| `GET /{realm}/users/{id}/groups`                        | [GroupCollection](src/Collection/GroupCollection.php)           | [Users::retrieveGroups()](src/Resource/Users.php)              |
-| `GET /{realm}/users/{id}/role-mappings/realm`           | [RoleCollection](src/Collection/RoleCollection.php)             | [Users::retrieveRealmRoles()](src/Resource/Users.php)          |
-| `GET /{realm}/users/{id}/role-mappings/realm/available` | [RoleCollection](src/Collection/RoleCollection.php)             | [Users::retrieveAvailableRealmRoles()](src/Resource/Users.php) |
-| `POST /{realm}/users/{id}/role-mappings/realm`          | `n/a`                                                           | [Users::addRealmRoles()](src/Resource/Users.php)               |
-| `DELETE /{realm}/users/{id}/role-mappings/realm`        | `n/a`                                                           | [Users::removeRealmRoles()](src/Resource/Users.php)            |
-| `PUT /{realm}/users/{id}/execute-actions-email`         | `n/a`                                                           | [Users::executeActionsEmail()](src/Resource/Users.php)         |
-| `GET /admin/realms/{realm}/users/{userId}/credentials`  | [CredentialCollection](src/Collection/CredentialCollection.php) | [Users::credentials()](src/Resource/Users.php)                 |
+| Endpoint                                                                             | Response                                                        | API                                                            |
+|--------------------------------------------------------------------------------------|-----------------------------------------------------------------|----------------------------------------------------------------|
+| `GET /admin/realms/{realm}/users`                                                    | [UserCollection](src/Collection/UserCollection.php)             | [Users::all()](src/Resource/Users.php)                         |
+| `POST /admin/realms/{realm}/users`                                                   | `n/a`                                                           | [Users::create()](src/Resource/Users.php)                      |
+| `GET /admin/realms/{realm}/users/{userId}`                                           | [User](src/Representation/User.php)                             | [Users::get()](src/Resource/Users.php)                         |
+| `PUT /admin/realms/{realm}/users/{userId}`                                           | `n/a`                                                           | [Users::update()](src/Resource/Users.php)                      |
+| `DELETE /admin/realms/{realm}/users/{userId}`                                        | `n/a`                                                           | [Users::delete()](src/Resource/Users.php)                      |
+| `GET /admin/realms/{realm}/users`                                                    | [UserCollection](src/Collection/UserCollection.php)             | [Users::search()](src/Resource/Users.php)                      |
+| `PUT /admin/realms/{realm}/users/{userId}/groups/{groupId}`                          | `n/a`                                                           | [Users::joinGroup()](src/Resource/Users.php)                   |
+| `DELETE /admin/realms/{realm}/users/{userId}/groups/{groupId}`                       | `n/a`                                                           | [Users::leaveGroup()](src/Resource/Users.php)                  |
+| `GET /admin/realms/{realm}/users/{userId}/groups`                                    | [GroupCollection](src/Collection/GroupCollection.php)           | [Users::retrieveGroups()](src/Resource/Users.php)              |
+| `GET /admin/realms/{realm}/users/{userId}/role-mappings/realm`                       | [RoleCollection](src/Collection/RoleCollection.php)             | [Users::retrieveRealmRoles()](src/Resource/Users.php)          |
+| `GET /admin/realms/{realm}/users/{userId}/role-mappings/realm/available`             | [RoleCollection](src/Collection/RoleCollection.php)             | [Users::retrieveAvailableRealmRoles()](src/Resource/Users.php) |
+| `POST /admin/realms/{realm}/users/{userId}/role-mappings/realm`                      | `n/a`                                                           | [Users::addRealmRoles()](src/Resource/Users.php)               |
+| `DELETE /admin/realms/{realm}/users/{userId}/role-mappings/realm`                    | `n/a`                                                           | [Users::removeRealmRoles()](src/Resource/Users.php)            |
+| `GET /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}`        | [RoleCollection](src/Collection/RoleCollection.php)             | [Users::retrieveClientRoles()](src/Resource/Users.php)         |
+| `GET /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}/available` | [RoleCollection](src/Collection/RoleCollection.php)          | [Users::retrieveAvailableClientRoles()](src/Resource/Users.php) |
+| `POST /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}`       | `n/a`                                                           | [Users::addClientRoles()](src/Resource/Users.php)              |
+| `DELETE /admin/realms/{realm}/users/{userId}/role-mappings/clients/{clientUuid}`     | `n/a`                                                           | [Users::removeClientRoles()](src/Resource/Users.php)           |
+| `PUT /admin/realms/{realm}/users/{userId}/execute-actions-email`                     | `n/a`                                                           | [Users::executeActionsEmail()](src/Resource/Users.php)         |
+| `GET /admin/realms/{realm}/users/{userId}/credentials`                               | [CredentialCollection](src/Collection/CredentialCollection.php) | [Users::credentials()](src/Resource/Users.php)                 |
 
 ### [Roles](https://www.keycloak.org/docs-api/26.0.0/rest-api/index.html#_roles)
 
diff --git a/src/Http/Client.php b/src/Http/Client.php
index d67d8c6..ef60c15 100644
--- a/src/Http/Client.php
+++ b/src/Http/Client.php
@@ -71,7 +71,7 @@ private function fetchTokens(): array
         try {
             $response = $this->httpClient->request(
                 'POST',
-                $this->keycloak->getBaseUrl() . '/realms/master/protocol/openid-connect/token',
+                $this->keycloak->getBaseUrl() . '/realms/' . $this->keycloak->getRealm() . '/protocol/openid-connect/token',
                 [
                     'form_params' => [
                         'refresh_token' => $this->tokenStorage->retrieveRefreshToken()?->toString(),
@@ -83,7 +83,7 @@ private function fetchTokens(): array
         } catch (ClientException $e) {
             $response = $this->httpClient->request(
                 'POST',
-                $this->keycloak->getBaseUrl() . '/realms/master/protocol/openid-connect/token',
+                $this->keycloak->getBaseUrl() . '/realms/' . $this->keycloak->getRealm() . '/protocol/openid-connect/token',
                 [
                     'form_params' => [
                         'username' => $this->keycloak->getUsername(),
diff --git a/src/Keycloak.php b/src/Keycloak.php
index e156cde..5f05a26 100644
--- a/src/Keycloak.php
+++ b/src/Keycloak.php
@@ -37,6 +37,7 @@ public function __construct(
         private readonly string $baseUrl,
         private readonly string $username,
         private readonly string $password,
+        private readonly string $realm = 'master',
         private readonly TokenStorageInterface $tokenStorage = new InMemory(),
         ?ClientInterface $guzzleClient = new GuzzleClient(),
     ) {
@@ -144,4 +145,9 @@ private function fetchVersion(): void
         $this->serializer = new Serializer($this->version);
         $this->commandExecutor = new CommandExecutor($this->client, $this->serializer);
     }
+
+    public function getRealm(): string
+    {
+        return $this->realm;
+    }
 }
diff --git a/tests/Unit/Http/ClientTest.php b/tests/Unit/Http/ClientTest.php
index 7189bbc..fdb433a 100644
--- a/tests/Unit/Http/ClientTest.php
+++ b/tests/Unit/Http/ClientTest.php
@@ -12,6 +12,11 @@
 use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\ClientException;
 use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\Psr7\Request;
+use GuzzleHttp\Client as GuzzleClient;
+use GuzzleHttp\Handler\MockHandler;
+use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Middleware;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 
@@ -114,4 +119,75 @@ public function testIsAuthorizedIfTokenStorageContainsUnexpiredAccessToken(): vo
 
         static::assertTrue($client->isAuthorized());
     }
+
+    public function testAuthenticatesUsingConfiguredRealm(): void
+    {
+        $accessToken = $this->generateToken((new DateTimeImmutable())->modify('+1 hour'));
+        $refreshToken = $this->generateToken((new DateTimeImmutable())->modify('+1 hour'));
+
+        $authorizationResponse = new Response(
+            status: 200,
+            body: json_encode(
+                value: [
+                    'access_token' => $accessToken->toString(),
+                    'refresh_token' => $refreshToken->toString(),
+                ],
+                flags: JSON_THROW_ON_ERROR,
+            ),
+        );
+
+        $realmsResponse = new Response(
+            status: 200,
+            body: json_encode(
+                value: [
+                    'realms' => [],
+                ],
+                flags: JSON_THROW_ON_ERROR,
+            ),
+        );
+
+        $history = [];
+        $historyMiddleware = Middleware::history($history);
+
+        $tokenRequest = new Request('POST', 'http://keycloak:8080/realms/custom-realm/protocol/openid-connect/token');
+        $mockHandler = new MockHandler([
+            new ClientException('Bad Request', $tokenRequest, new Response(400)),
+            $authorizationResponse,
+            $realmsResponse,
+        ]);
+
+        $handlerStack = HandlerStack::create($mockHandler);
+        $handlerStack->push($historyMiddleware);
+
+        $httpClient = new GuzzleClient(['handler' => $handlerStack]);
+
+        $keycloak = new Keycloak(
+            'http://keycloak:8080',
+            'admin',
+            'admin',
+            realm: 'custom-realm',
+        );
+
+        $client = new Client($keycloak, $httpClient, new InMemoryTokenStorage());
+
+        $client->request('GET', '/admin/realms');
+
+        // Verify that any token endpoint call uses the configured realm in the URL
+        static::assertNotEmpty($history);
+        $tokenCalls = array_values(array_filter((array) $history, function (array $transaction): bool {
+            /** @var Request $request */
+            $request = $transaction['request'];
+            return str_contains((string) $request->getUri(), '/protocol/openid-connect/token');
+        }));
+        static::assertNotEmpty($tokenCalls);
+        foreach ($tokenCalls as $transaction) {
+            /** @var Request $request */
+            $request = $transaction['request'];
+            $authUri = (string) $request->getUri();
+            static::assertStringContainsString('/realms/custom-realm/', $authUri);
+            static::assertStringNotContainsString('/realms/master/', $authUri);
+        }
+
+        static::assertTrue($client->isAuthorized());
+    }
 }