G. A. Cohen was one of the leading political philosophers of recent times. He first came to wide attention in 1978 with the prize-winning book Karl Marx's Theory of History: A Defence. In subsequent decades his published writings largely turned away from the history of philosophy, focusing instead on equality, freedom, and justice. However, throughout his career he regularly lectured on a wide range of moral and political philosophers of the past. This volume collects these previously unpublished lectures. Starting with a chapter centered on Plato, but also discussing the pre-Socratics as well as Aristotle, the book moves to social contract theory as discussed by Hobbes, Locke, and Hume, and then continues with chapters on Kant, Hegel, and Nietzsche. The book also contains some previously published but uncollected papers on Marx, Hobbes, and Kant, among other figures. The collection concludes with a memoir of Cohen written by the volume editor, Jonathan Wolff, who was a student of Cohen's. A hallmark of the lectures is Cohen's engagement with the thinkers he discusses. Rather than simply trying to render their thought accessible to the modern reader, he tests whether their arguments and positions are clear, sound, and free from contradiction. Throughout, he homes in on central issues and provides fresh approaches to the philosophers he examines. Ultimately, these lectures teach us not only about some of the great thinkers in the history of moral and political philosophy, but also about one of the great thinkers of our time: Cohen himself.