Experts, who were the sole active dispensers of certain kinds of knowledge in the days before AI, have now often assumed a rather passive role. They relay their knowledge to various novices, knowledge engineers, experimental psychologists or cognitivists - or other experts! - involved in the development and understanding of expert systems. This book achieves a perfect marriage between experimentalists and theoreticians who deal with expertise. It tries to establish the benefits to society of an advanced technology for representing and disseminating the knowledge and skills of the best corporate managers, the most seasoned pilots, and the most renowned medical diagnosticians. This book interests psychologists as well as all those out in the trenches developing expert systems, and everyone pondering the nature of expertise and the question of how it can be studied scientifically. Its scope, the pivotal concepts which it elucidates and brilliantly summarizes and appraises in the final chapter, as well as the references it includes, make this book a landmark in the field.