This book presents the oldest commentary on Aristotle written in Arabic, a compendium of De Generatione et Corruptione. Its author was the Imamite theologian Ibn M s al-Nawbakht (fl. ca. 900), of whom a single work (among more than forty ones recorded) was known to be extant. This new text sheds light both on the Greek tradition the author makes extensive use of Alexander s lost commentary and on the formative period of Shi ism.