David Malet Armstrong (8 July 1926–13 May 2014) has been one of the most influential contemporary metaphysicians working in the analytic tradition and surely the greatest 20th century Australian philosopher. His main merit is to have reestablished metaphysics as a respectable branch of philosophy placing it at the centre of the philosophical debate, and giving it the status of an authoritative and competent interlocutor of both rational and empirical sciences. By means of a rigorously argumentative approach and a sharp prose, Armstrong has built a whole metaphysical system, that is, a comprehensive and unified picture of the fundamental structure of the world. The various chapters of the book address the key issues concerning Armstrong' view about the problem of universals, the nature of states of affairs, the ontological ground of possibility, nomic necessity, and dispositions, the truthmaker theory, and the theory of mind. This volume aims to celebrate Armstrong’s memory bringing new understanding, and hopefully stimulating more work, on his philosophy, with the conviction that it constitutes an invaluable heritage for contemporary research in metaphysics.