What are the conceptual and practical territories of psychology? How have the boundaries of psychological thought, research and practice developed in history, and how might they be renegotiated today? This volume presents new approaches to these questions, resulting from a three-year collaboration among internationally known psychologists, neuroscientists, social scientists, and historians and philosophers of science from Germany and the United States under the auspices of the Berlin-Brandenburg Academy of Sciences and Humanities. The authors reflect critically on past and present views of psychology by focusing on three broad topic areas: How have psychological concepts been used in disciplines such as psychology, philosophy, or neuroscience, as well as daily life? Has the use of instruments in psychological research expanded or restricted the discipline’s reach? And, how have psychological thinking and research worked in practical contexts? The volume investigates separations between, as well as interactions among, psychology and its neighboring fields and tries to overcome disciplinary distinctions in exemplary ways. The contributions aim to make historical and philosophical studies of psychology relevant to contemporary concerns, and to show how psychology can profit from better interdisciplinary cooperation–thus improving mutual understanding between different scientific cultures.