During the last twenty years our understanding of expertise has dramatically increased. Laboratory analysis of chess masters, experts in physics and medicine, musicians, athletics, writers, and performance artists have included careful examination of the cognitive processes mediating outstanding performance in very diverse areas of expertise. These analyses have shown that expert performance is primarily a reflection of acquired skill resulting from the accumulation of domain-specific kwledge and methods during many years of training practice. The importance of domain-specific kwledge has led researchers on expertise to focus on characteristics of expertise in specific domains. In Toward a General Theory of Expertise many of the world's foremost scientists review the state-of-the-art kwledge about expertise in different domains, with the goal of identifying characteristics of expert performance that are generalizable across many different areas of expertise. These essays provide a comprehensive summary of general methods for studying expertise and of current kwledge about expertise in chess, physics, medicine, sports and performance arts, music, writing, and decision making. Most important, the essays reveal the existence of many general characteristics of expertise.