This paper presents the results of 38 case and field studies from 57 published papers spanning two decades of group support systems (GSS) research. It organizes the methodology and results of these studies into a four-factor framework consisting of contextual factors, intervening factors, adaptation factors, and outcome factors. The results show that the modal outcome for a GSS in field settings is to improve performance relative to manual or other methods as measured by effectiveness, efficiency, consensus, usability, and satisfaction in 91.5% of the cases. These are much more positive results than have been obtained in laboratory experiments. The reasons for the differences in findings and the research and development issues raised by the findings are explored.