Abstract: A viable concurrent engineering environment should support synchronous collaboration among distributed users. Shared window systems provide this support by allowing multiple users to create workstation-based conferences wherein conferees simultaneously view and manipulate shared files using existing, familiar applications. To be effective, a shared window system must be flexible and robust: one should be able to dynamically create conferences around applications that are already in use, new participants should be able to join conferences already in progress, and participants who become disconnected from a conference should be able to rejoin. We describe an efficient solution to the problem of making shared window conferencing flexible and robust. This general problem is phrased in terms of allowing a latecomer to join a conference. The essence of our approach is a protocol filtering and archival process that is tapped into the communication channel between a conference application and a user's display manager. This filter process interprets, in real-time, the application/display manager protocol stream and records the minimal information necessary to generate an exact replica of the application's interface on a remote display when a latecomer joins this conference. This solution has been implemented in XTV: a public domain shared window system based on the X Window System.