This book is the record of a debate that took place in the early tenth century between the famous Ismaili missionary Abū Hatim al-Rāzī and the even more celebrated Abū Bakr al-Razi , a physician and philosopher who was known to medieval Europe as “Rhazes.” These two were towering figures of premodern Islamic thought, and their debate over the dogmatic lines between Sunni and Shi’i theological positions serves to illuminate some of the most intellectually exciting topics of medieval Islamic culture. Abū Hatim, in particular, marshals evidence for his position from the Quran, the hadith, and pre-Islamic Arabic poetry as well as from the Jewish and Christian scriptures. This fresh, vivid debate still holds excitement for modern readers who are interested not merely in medieval Islam but in Christian thought as well.