The purpose of this Handbook is to provide a comprehensive picture of the field of Expertise Studies. We offer both traditional and contemporary perspectives, and importantly, a multidiscipline-multimethod view of the science and engineering research on expertise. We present different perspectives, theories, and methods of conducting expertise research, all of which have had an impact in helping us better understanding expertise across a broad range of domains. The Handbook also describes how researchers and practitioners have addressed practical problems and societal challenges. We have sought to demonstrate the heterogeneity of approaches and conceptions of expertise, to place current views of expertise in context, to show how these views can be used to address current issues, and to examine ways to advance the study of expertise.