This book collects Martin Wight’s works on the theory and philosophy of international politics. It includes classic works, such as “Why Is There No International Theory?” and “Western Values in International Relations,” as well as previously unpublished works such as “The Communist Theory of International Relations” and “Gain, Fear and Glory: Reflections on the Nature of International Politics.” These works encompass four categories: (a) traditions of thinking about international politics since the sixteenth century, (b) the causes and functions of war, (c) international and regime legitimacy, and (d) fortune and irony in international politics. Wight identifies and analyzes three major traditions of thinking about international politics in the West since the sixteenth century: Realism, Rationalism, and Revolutionism, also known as the Machiavellian, Grotian, and Kantian approaches. Wight examines the causes of war highlighted by Thucydides and Hobbes (material interest, fear, and reputation), and considers the functions of war in international politics (such as winning and retaining national independence and upholding the balance of power). Wight reviews the history of dynastic and popular legitimacy as well as post-1945 concepts of international and domestic legitimacy. Finally, Wight considers fortune and irony, including the decision-maker’s frequent rediscovery of the recalcitrance of events. Unintended, unexpected, and ironical consequences abound in international politics. This volume also features eight book reviews by Wight, including his assessments of works by Raymond Aron, E. H. Carr, Friedrich Meinecke, and Hans Morgenthau.