Abstract: The study on expert systems led to the identification of the ‘knowledge acquisition bottleneck,’ that it was generally extremely difficult to make overt the presumed knowledge of human experts in order to program it for computers. The history and reasons for the adoption of repertory grid methodologies and tools to overcome the knowledge acquisition bottleneck are described. Then a more fundamental analysis is made of why expert systems to date have had only limited success and merits of a personal construct approach to emulating human expertise in greater depth than has been achieved with existing cognitive science models are presented. In conclusion, it is noted that the techniques developed to emulate human expertise are essentially ones for modeling and emulating any person’s psychological processes, not just those of people valued by others as experts. PCP-based expert systems methods and technology have wide relevance, for example, in clinical and educational research and applications. The role of personal construct psychology in computer research and applications concerned with the development of expert systems and their beginnings in artificial intelligence and cognitive science are covered in this study.