At the basis of modern natural law theories, the concept of the suum, i.e. what belongs to the person (in Latin, his, her, its, their own), has received little scholarly attention despite its importance both in explaining and justifying not only the genealogy of property, but also that of morality and war. In this essay I focus on Grotius’s account of the suum and examine what it is, what things it includes, what rights it gives rise to, and how it is extended in the transition from the state of nature to civil society. I then briefly suggest that reviving this concept could help to illuminate the current discussion on the foundations of basic human rights, and to re-evaluate cases where these seem to clash with property rights.