An examination of Thomas Hobbes's Leviathan (1651), its contexts, the controversies surrounding its reception and some of the uses to which it has been put in the twentieth century. Leviathan is, by general consent, the most important work in political theory written in the English language; but it is more than a political theory; it is an argument about philosophy, science, language, human psychology and religion. It is a work of rhetoric and satire and is one of the great prose works of English. It thus evokes a range of contexts, of the Reformation, the Scientific revolution, the British and French Civil Wars, the humanism of the Renaissance. On publication it proved highly controversial. It was largely overlooked in the nineteenth century but in our own it has been re-discovered as central to the understanding of political civilisation. It is still as controversial, though for different reasons, as it was in the seventeenth century. Studying it is a way into our own civilisation as well as Hobbes's own world.