This dissertation concerns a cluster of related issues surrounding the Epicurean conception of justice. First, I show that the Epicureans defend a sophisticated kind of social contract theory and maintain a kind of legal positivism, views that are widely held today and so are of continuing interest for contemporary readers. In doing so, I argue that thinking about justice and law forms an integral part of Epicurean philosophy (pace the standard view). Second, I take up some neglected issues regarding justice and so provide detailed accounts of the metaphysics of moral properties in Epicureanism as well as of Epicurean moral epistemology. After the introduction in chapter 1, I set out the main features of the Epicurean view of justice and law in chapters 2-4. In chapter 2, I explain the basics of the Epicurean conception of justice as an agreement and relate it to Epicurean ethics as whole. In chapter 3, I examine Epicurean culture stories and I point out in what way the Epicurean view is a kind of social contract theory. In chapter 4, I argue that the most important aspect of the Epicurean conception of justice from a metaethical perspective is that justice, a moral fact, depends on benefit, a natural fact about the world. On the basis of this analysis, I subsequently argue that the Epicurean conception of the law is best understood as a kind of inclusive positivism. After having laid out the Epicurean view in this way, I enlarge the conversation in chapters 5-7. In chapter 5, I discuss the motivations Epicurean agents have to be just and comment on the relationship between contractual justice, that is, justice that comes about by agreements, and aretetic justice, that is, justice understood as a virtue or character disposition. In chapter 6, I turn to the metaphysics of justice, arguing that the just, for the Epicureans, is an accidental property. In chapter 7, finally, I show that Epicurean agents come to have an understanding of justice via sense experience in the same way that they have an understanding of everyday objects.