Thomas Hobbes is one of the first great modern philosophers. In developing a unified and comprehensive theory of the natural world, the nature of human beings, and politics, Hobbes's intellectual work ranged over philosophy, political theory, science, theology, history and mathematics. In particular, his version of the social contract theory is one of the enduring intellectual achievements of modern political and moral thought. This dictionary provides a comprehensive expository account of over one hundred and thirty key concepts covering the entire range of Hobbes's thought. Extensively cross-referenced, the volume also includes a biography of Hobbes, a chronology of his 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.