American Psychology and the Great War provides the first comprehensive examination of the research of psychologists during the Great War in early twentieth-century America, spanning efforts that produced a mix of successes, controversies, and unforeseen consequences. When the United States entered the Great War, psychologists seized an unprecedented opportunity to advertise the usefulness of their discipline to the military. They developed an ambitious set of plans to support the war effort, including large-scale intelligence tests on army recruits, personnel organization systems, identification of soldiers capable of managing emerging military technologies, and rehabilitation protocols for injured veterans. This study traces how psychologists navigated the complex process of establishing scientific credibility while delivering practical results under wartime pressures. It examines both their notable successes and significant controversies, analyzing how military psychology research subsequently influenced civilian applications, particularly in public education systems. By contextualizing wartime efforts within the broader development of applied psychology in the pre-war years, the book illuminates how psychological work with the military accelerated the transformation of the discipline from an academic curiosity into a profession with real-world applications. A unique and fascinating insight into the history of American psychology, this book is essential reading for scholars in the history of psychology and early twentieth-century American social and intellectual history.