In this chapter we present some of our results concerning source models for H.261 coded VBR (variable bit rate) video. Video services have been forecasted to be a substantial portion of the traf®c on emerging broadband digital networks. Statistical source models of video traf®c are needed to design networks that delivery acceptable picture quality at minimum cost, and to control and shape the output rate of the coder. For example, one issue is deciding whether a new video connection can be admit