Google Apps Administrative APIs allow developers to write applications to manage Google Apps domains, as well as migrate from and integrate with existing IT infrastructure, create users, update settings, audit activity, and more.
Many other Google Apps Administrative APIs are based on the Atom and RSS syndication formats and the Atom publishing protocol, and also include support for authentication, querying, and version conflict detection. Client libraries are available in a variety of popular languages.
To get started with Google Apps Administrative APIs, dive into the API-specific documentation. You'll find detailed reference documentation, how-to guides, discussion forums, and other helpful resources.