An efficient conference service facilitates the implementation and the run-time control of conference applications. Key features of a conference service are conference management, multicast communication support, application state synchronization, user data marshalling and scalability. The paper defines a conferencing service to fulfil these requirements of conferencing applications. The conference control protocol, which is used for our conferencing service, is described in its main parts like topology, reconfiguration and multipoint transfer. An object model of the service is proposed together with the resulting architecture. A multipoint platform is introduced as a case study. Greetings