Proponents of global egalitarian justice often argue that their positions are compatible with the principle of self-determination. At the same time, prominent arguments in favor of global egalitarianism object to one central component of the principle: namely, that the borders of states (or other political units) are normatively significant for the allocation of rights and duties; that duties of justice and democratic rights should stop or change at borders. In this article, I propose an argument in defense of the normative significance of territorial boundaries that draws on a political interpretation of the principle of self-determination. The political interpretation is distinct from the two major approaches to self-determination: the national and the democratic. It makes a twofold contribution to the debates about global justice and democracy; while it (a) challenges the position that political memberships and political borders are morally arbitrary; it (b) helps define the realm of permissible autonomy for self-governing political units, which does not ignore duties to nonmembers and outsiders.