Written in English, this book contains the editio princeps, the translation, and commentary of an anonymous Arabic commentary on Aristotle’s treatise On generation and corruption. Although this treatise has to date escaped the notice of historians of Arabic philosophy, it is nevertheless of considerable interest. If the date that the author suggests for the work is retained—around the year 900 AD—then not only is it the oldest surviving Arabic commentary on Aristotle, but also a unique remnant of a very little known period of the history of philosophy: the century separating the activity of al-Kindī (ca 800–after 860) from that of al-Fārābī (870–951).