The present invention provides an application programming interface ("API") to address book management functions for accessing and managing an integrated online address book clearinghouse. The API receives function calls from applications and executes one or more functions in response to the function calls. The address book functions manage address books of the integrated online address book clearinghouse by adding, deleting, updating, and finding address books, contacts, and groups of contacts of the address books. The API also verifies identity information to assure that each function call has authorization to access the desired address book. The API further includes a parameter processing module for processing function-specific parameters passed in data envelopes to the API by the applications. The API also includes a response generating module for responding to the application that sent a function call to the API.