Considered the father of modern American anthropology, Franz Boas introduced the relativistic, culture-centered methods and principles of inquiry that continue to dominate the field. This study analyzes the development of his thought and his contributions to racial and ethnic theory in the context of his own ethnicity and personal experience with persecution. The author focuses primarily on Boas's attempt to fuse science with political and social activism—an effort to insure that his ideological contributions to science had practical relevance to the difficult issues facing American society. Hyatt fills in the details of Boas's background, from his early years in Germany to his emigration to the United States in the late 1880s, and discusses his pivotal role in transforming anthropology from an amateur pursuit into a rigorous academic discipline. The author examines Boas's attacks on those who used science to promulgate theories of racial inferiority based on alleged differences in mental ability. He traces the origins of Boas's own theories and the use he made of them in working for equal rights for immigrants and African Americans. This is the first biographical study to focus on the historical meaning of Boas's contributions and the motivating forces that shaped his work. Essential for courses in race and ethnicity, sociology, the history of anthropology, 20th-century American history, American intellectual history, theories of culture, and related subjects.