This volume reconstructs Martin Heidegger’s lecture course at the University of Marburg in the winter semester 1924–25, devoted to an interpretation of Plato (especially his later dialogue, the Sophist) and Aristotle, especially Book VI of the Nichomahcan Ethics. Published for the first time in German in 1992 as volume 19 of Heidegger’s Collected Works, it is one of Heidegger’s major texts, because of its intrinsic importance as an interpretation of Aristotle and Plato and also because of its relation to Being and Time. Composed at the same time, the lectures and Being and Time are complementary works in that both are commentaries on Plato’s Sophist. The lectures approach Plato through a detailed reading of the Nichomachean Ethics, providing one of Heidegger’s major interpretations of Aristotle. In a line-by-line interpretation of the Sophist, Heidegger then takes up the relation of Being and non-being, the ontological problematic that forms the key link between Greek philosophy and Heidegger’s thought.