The Rapport multimedia conferencing system supports interactive, real-time, distributed conferences among two or more people. Executing on personal workstations interconnected by data and voice networks, Rapport provides basic mechanisms to create, manage, and terminate conferences. The authors focus on the Rapport software, which is a three-level hierarchy comprised of the user interface, conference server, and system levels. The user interface level provides humans and other programs with access to the Rapport system. Maintaining consistent views of the conference for all the participants, the conference server level coordinates the activities of the conferees and provides basic protocols for exchanging information and control during a conference. The system level includes window management service and drivers for the hardware required to transmit data in the various media.