Herbert Simon (1969) set out an ambitious programme of research for a science of design. This thesis examines the routes taken and the problems encountered with this programme as it is found in the flagship domain of Human-Computer Interaction. It examines the emergence of Human-Computer Interaction as a discipline and its problems (Chapter 1). It considers recent attempts to reformulate many of the foundations of HCI's design theory (Chapter 2) including work of my own (Chapter 3). It describes the development of a new field of Computer-Supported Cooperative Work (Chapter 4) and a new approach to understanding the environment from a social rather than a cognitive point of view by using ethnographic methods imported from sociology and social anthropology and now closely associated with the field of CSCW (Chapter 5). This new orientation is seen by many to offer new hope for informing design and overcoming some of the problems that have so far beset HCI. It represents one of the most significant contributions to design to have emerged from sociology and social anthropology. It is not, however, without its own difficulties in terms of being able to effectively 'speak to' the design process. Ethnographic methods have also been used to examine the very process of design itself and I report on a number of such studies and some of the issues which they raise (Chapter 6). In particular I will report in detail on an ethnographic study of my own which sought simultaneously to investigate the worth of this research orientation, to understand some of the ways in which ethnographic studies can contribute to system design and particularly the design of CSCW technologies and to do this through a study of another area of design work - fashion design (Chapter 7). Studies such as this of design in practice do, however, raise a number of challenging issues for the type of science of design envisaged by Simon and his associates. Empirically examining what design is and how design is done questions some of the abstract formulations of design. Additionally, I suggest that some care is needed in schematizing how a method such as ethnography can contribute to a design process. I consider these results in my concluding chapter (Chapter 8) where I argue that the ethnographic approach turns out to contrast fundamentally with Simon's view of design for his conception of design is also crucially a perspective upon action itself. It is this perspective which ultimately motivates Simon to claim that the proper study of mankind is the science of design, while it is an ethnographic orientation which motivates me to argue that design is practical action and that practical action is designed.