Abstract: This paper deals with the problem of allowing a participant to dynamically join and leave a computer-based conference that is already in progress. A conference is a synchronous collaboration session where participants at remote locations are cooperating through identical copies of windows generated by applications shared by all conference participants. In this paper, an efficient solution to the problem of accommodating a latecomer is found by recording the modifications to the window system's state implied in the series of commands generated by the applications, and later imposing these state modifications on a latecomerUs window system.