Free Google+ API eBook - Google+ API
The Google+ API is the programming interface to Google+. You can use the API to integrate your app or website with Google+. This enables users to connect with each other for maximum engagement using Google+ features from within your application.
Applications are limited to a courtesy usage quota. This should provide enough access for you to preview the API and to start thinking about how you want to build your application.
Many API calls require that the user of your application grant permission to access their data. Google uses the OAuth 2.0 protocol to allow authorized applications to access user data.
Most of the Google+ API follows a RESTful API design, meaning that you use standard HTTP methods to retrieve and manipulate resources. For example, to get the profile of a user, you might send an HTTP request like: