This volume presents a selection of David Gauthier's writings on Thomas Hobbes (1588-1679) and the theory of political contractarianism. The eight essays on Hobbes, written over four decades, represent the author's changing understanding of the moral and political theories since the publication of The Logic of Leviathan (OUP, 1969). These include essays on Hobbes on law, challenging influential readings of his legal philosophy, and a previously unpublished piece, 'The True and Only Moral Philosophy', providing a close reading of chapters 13-15 of Leviathan. The four essays on social contract theory include an extended version of 'Political Contractarianism' (1997), Gauthier's well-known 'Public Reason' (1994), and a paper previously available only in French and Spanish translations.