This is the only commentary on Aristotle's theological work, Metaphysics, Book 12, to survive from the first six centuries CE - the heyday of ancient Greek commentary on Aristotle. Though the Greek text itself is lost, a full English translation is presented here for the first time, based on Arabic versions of the Greek and a Hebrew version of the Arabic. In his commentary Themistius offers an extensive re-working of Aristotle, confirming that the first principle of the universe is indeed Aristotle's God as intellect, not the intelligibles thought by God. The identity of intellect with intelligibles had been omitted by Aristotle in Metaphysics 12, but is suggested in his Physics 3.3 and On the Soul 3, and later by Plotinus. Laid out here in an accessible translation and accompanied by extensive commentary notes, introduction and indexes, the work will be of interest for students and scholars of Neoplatonist philosophy, ancient metaphysics, and textual transmission.