Contacts are relationships that exist in your Yahoo! address book, such as those entered from across the Yahoo! Network like Yahoo! Mail and Yahoo! Messenger. The API enables your application to leverage those relationships by reading a user's Contacts information safely and securely, respecting that user's privacy and permission settings.
In order to access Contacts data in your application, you’ll need to get a Yahoo! API key and configure it to use Contacts. You can do this by creating a project for your application.
Previous versions of the Contacts API utilized a Web Service as a way to access user's Contacts data. Documentation for the previous Contacts web service remain available, including a screencast explaining its use and the PHP and Flash SDKs.
Learn how to use the Contacts API through descriptions of its queries and parameters. In addition, the documentation also inculdes sample code to help get you started.
Join the conversation on the Contacts developer forum to get help and touch base with other developers.