The study of expertise has led to considerable insight into the nature of skilled performance in professional domains. However, much of this research remains to be exploited in developing computer systems to improve decision making in professional practice. This presentation will discuss application of an approach known as cognitive task analysis for examining how physicians cope with decision complexity. Cognitive task analysis can be used in characterizing the skills, strategies and problems of decision makers in dealing with decision situations of varied complexity. Examples will be provided which describe application of cognitive task analysis along a continuum ranging from in-depth analysis of physician's decision making, as a basis for selection of decision support, to its application in the development and evaluation of computer tools to support human cognition. In this presentation, it will be shown that an in-depth understanding of human cognitive processes will be needed in order to develop more effective computer systems in health care.