This book offers a critical analysis of the Sanskrit, Syriac, and Persian sources in Abū Bakr Muḥammad ibn Zakariyyā al-Rāzī’s (born 251 AH / 865 AD, died 313 AH / 925 AD) Comprehensive Book of Medicine (Arabic title al-Kitab al-Hawi fi l-Tibb). Al-Razi (latinized Rhazes) was an Iranian scholar from Rayy, a true polymath who wrote his various works on medicine, alchemy, and philosophy mainly in Arabic; he ranks among the most versatile and most authoritative thinkers in the history of Islam, and certainly belongs to the greatest exponents of the Iranian scientific tradition. The Comprehensive Book is the most distinguished and most important of his many works: a medico-pharmaceutical encyclopedia of enormous proportions, containing medical information from Greek, Syriac, Persian, and Sanskrit sources, and constituting a unique mine of information that is unmatched not only in Islamic but also in world literary history.