Thomas Hobbes is one of the first great modern philosophers. In particular, his version of the social contract theory has proved to be one of the enduring intellectual achievements of modern political and moral thought. This dictionary provides a comprehensive and cohesive expository account of about one hundred and fifty key concepts covering the entire range of Hobbes's thought, from philosophy, political theory and science, to theology, history and mathematics. Extensively cross-referenced, the volume also includes a biography of Hobbes, a chronology of Hobbes's life and works, a chronology of historical events in the early and mid-seventeenth century, and an annotated bibliography of Hobbes's major works, contemporary editions, and main secondary literature. This volume will be indispensable for students and researchers interested in Hobbes's life and thought.