The purpose of this paper is to suggest a comparative morphology of groups which would be applicable to the whole of social scientific research. The key to the morphological classes suggested is not a focus on the group system itself but on its relationship with the next higher system--the group system's environment. The information exchange between the group and its environing system provides the group system with its energizing life force, i.e., tensity. The precise nature of that information exchange differentiates among classes of tensity. The morphological classes--extensive, intensive, detensive, distensive, and attensive--are described and illustrated. Preliminary empirical testing through correlations of interaction analyses of five groups suggests that it is possible to differentiate among tensive classes by differences in interaction patterns. The data suggest further that groups not possessing a specific variety of tensity can be identified through their interaction patterns as belonging to a specific tensive class. Results from preliminary empirical analyses suggest numerous implications for further research in order to integrate and increase the ability to generalize group research. (Author/WR)