Decision groups have assumed new and expanded roles as a result of the application of electronic technologies such as group DSS. The rational selection and assignment of members to a computer‐supported group is an important research issue with significant implications for organizational effectiveness. Formal group‐composition models are developed for knowledge‐based and coalition‐formation decision tasks. In the context of these models, group properties of synthesis, redundancy, and synergy are defined and related to concepts for rational selection of group members. Conceptual and operational constructs are presented, providing a practical foundation for initiating detailed analysis of interactions between group‐composition and group‐decision processes. Implications for future research are discussed.