Multiple contact lists of a user, which individual lists are maintained in varying formats associated with varying internet-based services or computer-based applications, are federated through the use of an intermediate schema used by a federating messenger application. The federating messenger application may be instantiated as a client resident at a computer system and/or as a server-based application accessible via a Web browser or dedicated client application. In one instance, the federated messenger application includes both client-based and server-based components, and on the client-side may be resident as a browser extension or similar application.