Philipp Frank (1884-1966) was an influential philosopher of science, public intellectual, and Harvard educator whose last book, The Humanistic Background of Science, is finally available. Never published in his lifetime, this original manuscript has been edited and introduced to highlight Frank’s remarkable but little-known insights about the nature of modern science-insights that rival those of Karl Popper and Frank’s colleagues Thomas Kuhn and James Bryant Conant. As a leading exponent of logical empiricism and a member of the famous Vienna Circle, Frank intended his book to provide an accessible, engaging introduction to the philosophy of science and its cultural significance. The book is steadfastly true to science; to aspirations of peace, unity, and human flourishing after World War II; and to the pragmatic philosophies of Charles S. Peirce, William James, and John Dewey that Frank embraced in his new American home. Amidst the many recent surveys and retrospective analyses of midcentury philosophy of science, The Humanistic Background of Science offers an original, first-hand view of Frank’s post-European life and of intellectual dramas then unfolding in Chicago, New York City, and Boston.