Abstract: The paper describes two approaches to supporting collaborative authoring of large-scale documents by teams of geographically distributed authors. The first approach provided synchronous support via multimedia conferencing, which allows authors to have virtual meetings. A case study of this approach led to the conclusion that it was an effective, but not necessarily efficient way of supporting the entire collaborative writing process. In the second approach, asynchronous support was offered to a number of authoring teams through the MESSIE environment. The system integrates automatically answered electronic mail, shared file store administration, and a version control tool in a UNIX enviroment. In a long-term field trial, MESSIE turned out to be an extremely powerful collaboration tool. Authors liked it because it allowed them to continue using their own tools, and only required them to learn a small number of commands. Three major conclusions are drawn from the two studies: (1) synchronous collaboration support is most effective during the initial and integration/reviewing stages of collaborative authoring; (2) asynchronous collaboration support can help to improve efficiency of collaboration in authoring team, especially document management; and (3) both approaches can be enhanced if the authoring team adopts explicit task-related collaboration strategies, or human protocols, to guide the collaboration process.