An extensible group decision-support system (GDSS) is proposed. The system would be a modular and modifiable system, as opposed to a complete GDSS intended to handle all decision settings. A GDSS for a specific decision setting would be supported by building extensions onto a kernel of capabilities. These extensions are expected to be built by a system specialist, and not by any member of the group. The proposed architecture, which is object-oriented, is shown to meet the requirements identified for a GDSS.