This history of ideas in American psychology divides 11 decades into three periods, marked out by specific themes central to psychologists over the years. Initially, the legacy of mind-body dualism challenged scientists to make coherent a single universe of mental and physical phenomena, but efforts were hampered by languages that embody mental, physical, and metaphysical commitments. This struggle began with James, whose work remains enormously relevant, is exacerbated by Titchener, whose mentalism provokes a reaction by Watson, whose physicalistic bias provoked a vastly expanded realm opened by Gestalt.The second period, from Freud to Skinner, shifted the focus from mind and body to experimental and clinical settings for the acquisition and application of psychological knowledge. Tolman, Hebb, Rogers, Hull, Piaget, and Skinner each sought to create a psychology that could bridge these two settings, often reducing one to the other, but often inventing ideas for psychology that vastly changed the earlier preoccupation with mind-body dualism. In the third period, feminists, phenomenologists, and post modern thinkers recentered psychology. The cultural acceptance of psychology as a point of view on virtually any issue led to a proliferation of diversity even greater than in the second period. The integration of psychology into employment roles in most segments of society made psychology more diverse and less unified than ever. An important resource for all scholars, students, and researchers involved with the history of ideas and American psychology.