This article is concerned with an analysis of the requirements for text-based on-line conferencing. From a system perspective, text-based on-line conferencing can be viewed as either message passing or data sharing. These complementary views give rise to different design dimensions. For example, the message-passing view is concerned with granularity, channels, message labels, and so on. The data-sharing view is concerned with the access different individuals have to the text: read only, appending, editing, pointing, and so on. A deliberately sparse prototype was built and placed in this design space. This minimal prototype has limited functionality so that the real problems experienced by users can show through. Relevant literature from disciplines such as social psychology, conversational analysis, and linguistics is briefly reviewed in terms of three generic communication tasks: synchronizing communication, maintaining structural coherence, and maintaining referents. © 1993, Taylor & Francis Group, LLC. All rights reserved.