During the past twenty years, our knowledge about expertise has dramatically increased. Laboratory analyses of chessmasters, experts in physics, medicine, international-level musicians, athletes, writers, and performance artists have allowed us to carefully examine 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 knowledge and methods during many years of training and practice rather than special innate talent. Confronted with universal limits of human information processing concerning memory capacity and speed of processing, expert performers are found to be able to acquire similar types of skills to circumvent these limits. General findings on expertise are systematized to lay the foundation of a general theory of expertise. In this book, many of the world's foremost scientists studying expert performance in specific domains of expertise review the state-of-the-art knowledge about expertise in these domains with the goal of identifying characteristics of expert performance that can be generalized across many different areas of expertise. These papers provide a comprehensive summary of general methods to study expertise and the current knowledge about expertise in chess, physics, medicine, sports, performing arts, music, writing, and decision-making. Most importantly, they reveal the existence of many general characteristics of expertise.