Saadya ben Joseph al-Fayyumi (882-942), gaon (head) of the rabbinic academy at Sura and one of the pre-eminent Jewish thinkers of the medieval period, attempted to create a complete statement of Jewish religious philosophy in which all strands of philosophical thought were to be knit into a unified system. In 'The Book of Doctrines and Beliefs', Saadya sought to rescue believers from 'a sea of doubt and the waters of confusion' into which they had been cast by Christianity, Islam, and other faiths. By employing philosophical -- or kalamic -- argumentation to examine and defend traditional Jewish beliefs, Saadya hoped to turn blind faith into conviction based on rational understanding. First published in 1946, and reprinted here without alteration, Alexander Altmann's judicious abridgement of his own translation has remained the standard edition of this influential work. A new Introduction by Daniel Frank sets Saadya's work in its broader historical, cultural, and philosophical contexts.