A solid grasp of the main themes and arguments of the seventeenth-century philosopher Rene Descartes is essential for understanding modern thought, and a necessary entree to the work of the Empiricists and Immanuel Kant. It is also crucial to the study of contemporary epistemology, metaphysics, and philosophy of mind. This new edition of Georges Dickers commentary on Descartess masterpiece, Meditations on First Philosophy, features a new chapter on the Fourth Meditation and improved treatments of the famous cogito ergo sum and the notorious problem of the Cartesian Circle, among numerous other improvements and updates. Clear and accessible, it serves as an introduction to Descartess ideas for undergraduates and as a sophisticated companion to his Meditations for advanced readers. The volume provides a thorough discussion of several basic issues of epistemology and metaphysics elicited from the main themes and arguments of the Meditations. It also delves into the works historical background and critical reception. Dicker offers his own assessments of the Cartesian Doubt, the cogito, the causal and ontological proofs of Gods existence, Cartesian freedom and theodicy, Cartesian Dualism, and Descartess views about the existence and nature of the material world. The commentary also incorporates a wealth of recent Descartes scholarship, and inculcates -- but does not presuppose -- knowledge of the methods of contemporary analytic philosophy.