The Web now enables people in different places to view three-dimensional models of buildings and places in a collaborative design discussion. Already design firms with offices around the world are exploiting this capability. In a typical application, design drawings and models are posted by one party for review by others, and a dialogue is carried out either synchronously using on line streamed video and audio, or asynchronously using email, chat room, and bulletin board software. However, most of these systems do not allow designers to embed annotations and proposed design changes in the threedimensional design model under discussion. We present a working prototype of a system that has these capabilities and describe the configuration of Web technologies we used to construct it.