John Leslie Mackie (1917-1981) was one of the most influential philosophers of the twentieth century. His published works spanned many areas, but he is not well known as a political philosopher. In the late 1970s, however, Mackie turned his attention to issues concerning justice. In a series of writings, Mackie built a case for a unique right-based approach to political philosophy, in part by delivering incisive critiques of theories dominant at the time. His most comprehensive work in this area is Theories of Justice and Rights--a previously unpublished manuscript that finally sees the light of day in this volume. Also included are two of Mackie's previously published papers, written during the same period: 'Can There Be a Right-Based Moral Theory?' (1978) and 'Rights, Utility, and External Costs' (1985). Some of Mackie's arguments in these works draw on the metaethical conclusions in his seminal book Ethics: Inventing Right and Wrong (1977). The editorial introduction canvasses the initially puzzling relation between Mackie's moral error theory and his account of justice and rights, addresses some exegetical queries, and connects to present-day debates. In addition, the introduction provides summaries of Mackie's theory of rights, his critique of Rawls's liberalism, and of Nozick's libertarianism.