This book has grown out of a series of public lectures delivered in the spring of 1945 in the Division of the Humanities of the University of Chicago. It proposes to outline the cultural orientation of the Muslim Middle Ages, with eastern Islam as the center of attention. It attempts to characterize the medieval Muslim's view of himself and his peculiarly defined universe, the fundamental intellectual and emotional attitudes that governed his works, and the mood in which he lived his life. It strives to explain the structure of his universe in terms of inherited, borrowed, and original elements, the institutional framework within which it functioned, and its place in relation to the contemporary Christian world.