A pioneering work in psychology, this enormously influential book served as a catalyst in the study of the foundations of social behavior. Ironically, its approach marked such a dramatic departure from contemporary trends that it stimulated little follow-up research at the time of its 1908 publication. In recent years, however, the author’s ideas have been resurrected in sociobiological reasoning, making the republication of this systematic treatise particularly timely. McDougall’s work grounds social behavior in biology, focusing on the individual and attributing most social behavior to instinct. This reasoning makes his work one of the first in modern psychology to take human motivation as its central concern. As one of the initial texts of social psychology, it assisted in laying the foundations of a new discipline, separating the field from its forerunners, sociology and general psychology. McDougall’s emphasis on the instinctive basis of social phenomena also helped promote the individualistic approach typical of modern social psychology. Popular, long-lived, and ever-relevant, this landmark work is guaranteed a wide audience among teachers and students of psychology.