This paper presents a review of the empirical studies of human-to-human communication which have been carried out over the last three decades. Although this review is primarily concerned with the empirical studies of computer supported human-to-human communication, a number of studies dealing with group work in non-computer-based collaborative environments, which form the basis of many of the empirical studies of the recent years in the area of CSCW, are also discussed. The concept of person and task spaces is introduced and then subsequently used to categorise the large volume of studies reported in this review. This paper also gives a comparative analysis of the findings of these studies, and draws a number of general conclusions to guide the design and evaluation of future CSCW systems.