In these essays, one of the most eminent political scientists of our time examines international relations from a variety of perspectives connected by timeless and common themes: the conflict between die ever-present risk of violence and the quest for international order, the tensions between the imperatives of power and those of morality, the ties that bind domestic and foreign policy, the ambiguities of the nuclear revolution, the break between prenuclear and post-1945 politics, and the dangers created by the competition between the nuclear superpowers. Assessing the development of the discipline of international relations, the author presents both a summary of the field's significant findings and a critical discussion of its most representative traditions of realism and liberalism. Written between 1960 and 1985, many of these essays have not been previously published in English. They reflect the author's own intellectual evolution and represent a complete picture of his approach to the study of world politics.