The Constant Contact APIs allow you to manage contacts in your account in various ways. By utilizing contacts collection and resource, you can add, edit, unsubscribe contacts as well as modify their contact list memberships. The Constant Contact REST API contains several useful methods to enable developers to easily manage contacts. For more informaiton, see the links below.
NOTE: The various elements in the Contact XML used to create and update contacts are subject to field length limitations. Please see the Contacts Collection and Resource reference for details. XML that violates these field length constraints will be rejected.