In HCI research and development, we remain faced by the long-standing problem that the development of a theoretical science base has lagged behind more intuitive systems design. Cognitive psychology had an important early influence on HCI, providing a strong theoretical base on which to draw. In recent years, HCI has expanded its focus on groups of users using computers to support collaborative work. This more recent research has drawn more widely on social and cognitive psychology and on disciplines such as anthropology. However, the relationship between the theoretical models of these disciplines and the practice of HCI design is not straightforward. As the scope of HCI has expanded from its earlier areas of strength in the cognitive tradition, the development of a solid, unifying theoretical base has not kept pace.