diff --git a/src/SubscribePro/Http.php b/src/SubscribePro/Http.php
index db11f95..f8a4814 100644
--- a/src/SubscribePro/Http.php
+++ b/src/SubscribePro/Http.php
@@ -35,6 +35,11 @@ class Http
      */
     public const DEFAULT_LOG_MESSAGE_FORMAT = "{method} - {uri}\nRequest body: {req_body}\n{code} {phrase}\nResponse body: {res_body}\n{error}\n";
 
+    /**
+     * User agent string for outgoing API requests.
+     */
+    public const USER_AGENT = 'subscribepro-php/1.1';
+
     /**
      * @var string
      */
@@ -86,6 +91,9 @@ protected function createClient()
             RequestOptions::HTTP_ERRORS => false,
             RequestOptions::AUTH => [$this->app->getClientId(), $this->app->getClientSecret()],
             RequestOptions::TIMEOUT => $this->requestTimeout,
+            RequestOptions::HEADERS => [
+                'User-Agent' => self::USER_AGENT,
+            ]
         ]);
     }