What does it mean for someone to have a moral right to something? What kinds of creatures can have rights, and which rights can they have? While rights are indispensable to our moral and political thinking, they are also mysterious and controversial; as long as these controversies remain unsolved, rights will remain vulnerable to skepticism. Here, Sumner constructs both a coherent concept of a moral right and a workable substantive theory of rights to provide the moral foundation necessary to dispel such doubts.