For over five centuries, the idea that people own themselves has appeared in philosophical work on justice. But the meaning of self-ownership has changed significantly over time, albeit largely unnoticed. Nowadays, philosophers usually understand self-ownership as a robust set of property-like rights over oneself, and chiefly they have debated whether such rights do or do not rule out certain forms of state redistribution of resources.By contrast, self-ownership first entered our philosophical tradition as a fundamental right to obligate others to interact with one according to shared norms by which persons are reciprocally bound. So understood, self-ownership bears on justice as primarily concerning how we treat one another, and in particular what it means to treat one another as equals.This book is an attempt to recover this earlier, yet now-novel, understanding of self-ownership. It undertakes four main tasks: to illustrate how this understanding of self-ownership makes possible a unified understanding of ownership generally; to trace and diagnose the shift in understandings of self-ownership over time; to illuminate self-ownership as a basic moral relation between persons; and to sketch how this new, old understanding of self-ownership reframes questions about justice. Owning Oneself offers a renewed framework for rethinking what we owe one another.