This paper takes an historical overview of the field of Human-Computer Interaction. It describes how the cognitive psychology emphasis on user involvement in systems development of the 1980s reached its limit by the early 1990s. At this point the focus shifted onto support for the tasks of users using computer-based systems in real contexts, a focus that ideally suits the mobile, ubiquitous and social technologies of the new millennium. The Cultural-Historical Activity Theory provides an appropriate framework for understanding this phenomenon and is adopted in this paper to present the work, over a seven year period, of a usability laboratory grounded in Activity Theory principles.