The “MBone” is the portion of the Internet that has implemented a new computer network technology called “multicasting”. Multicasting supports efficient distribution of network traffic to multiple users simultaneously. Videoconferencing is the most common MBone application in use today and this paper reviews the human factors issues related to MBone videoconferencing. Three parameters of human factors concerns are defined: the task of the session (meeting, education, entertainment), the media used during the session (video, audio, shared workspace), and the communication modes involved (interactive vs. non-interactive and formal vs. informal). Videoconference sessions and software can be placed in this parameter space and this can provide valuable information about the technical and human requirements. The human factors research literature relevant to each of these parameters is reviewed and the current MBone tools are analyzed. Specific recommendations are made for MBone session organizers and software developers. These recommendations are not all specific to multicasting and will be of interest to people developing or using any videoconference system.