The Internet was designed mainly for non-real-time data, and the existing error recovery mechanisms cannot be used for time critical applications because of their latency. Therefore, any real-time interactive application will need to be robust to packet losses caused mainly by congestion at routers, and this is especially true for video transmissions. In this paper, the problem of robust H.263# video over the Internet is addressed. The e!ect of packet loss on H.263 (version 2) video transmitted over the Internet using the real-time transport protocol (RTP) is assessed and di!erent packetisation strategies are also compared. The main problem is the temporal propagation of errors resulting from packet losses because of the motion compensation process. Two ways of minimising this propagation are proposed: the selective use of FEC on the motion information and the use of periodic reference frames, protected with FEC as well. The main advantage of these two techniques is that they do not introduce more than one frame delay, and they do not rely on retransmissions. When combined together, these are shown to perform better than using periodic intraframes at minimising error propagation. Our robust H.263# encoder has been integrated into vic, a videoconferencing tool widely used over the multicast backbone (MBone) of the Internet.