In this volume Simplicius deals with Aristotle's account of the Presocratics, and for many of them he is our chief or even sole authority. He quotes at length from Melissus, Parmenides and Zeno, sometimes from their original works but also from later writers from Plato onwards, drawing particularly on Alexander's lost commentary on Aristotle's Physics and on Porphyry. Much of his approach is just scholarly, but in places he reveals his Neoplatonist affiliation and attempts to show the basic agreement among his predecessors in spite of their apparent differences. This volume, part of the groundbreaking Ancient Commentators on Aristotle series, translates into English for the first time Simplicius' commentary, and includes a detailed introduction, extensive explanatory notes and a bibliography.