In contrast to the vast literature on retributive theories of punishment, discussions of private revenge are rare in moral philosophy. This paper reviews some examples, from both classical and recent writers. It detects, both in the philosophical tradition and in contemporary moral discourse, uncertainty and equivocation over the ethical significance of acts of revenge, and in particular over their possible resemblances, in motive, purpose or justification, to acts of lawful punishment. A key problem for the coherence of our ethical conception of revenge, it suggests, is the consideration that certain acts of revenge may be just (at least in the minimal sense that the victim of revenge has no grounds for complaint against the revenger) and yet be generally agreed to be morally wrong. It argues that the challenge of explaining adequately why private revenge is morally wrong poses particular difficulty for purely retributive theories of punishment, since without invoking consequentialist reasons it does not seem possible adequately to motivate an objection to just and proportionate acts of revenge. The paper concludes by identifying some of the directions in which further reflection on the moral and political significance of revenge might proceed.