By early 1996, approximately 140 different controlled experiments had been published in 164 articles in refereed journals or conference proceedings, which examined processes and outcomes in computer- supported group decision making. This paper is a concise overview of what has been studied and how: the systems, independent and intervening variables manipulated or measured, and experimental procedures employed. A subsequent paper will examine the dependent variables and findings of the experiments. The purpose is not only to provide a comprehensive summary of past research, but also to critically assess what has been studied little or inadequately, in order to inform design choices for future experiments.