We speak of rights as though they are objective matters of fact that have a crucial bearing on how we ought to behave. Yet few, if any, rights are universally acknowledged without wide differences of meaning. Instead, they usually represent the particular ideals of the individuals or groups that claim them. Theories of rights have always grappled with this central problem, but none of the literature on the subject has offered a satisfactory solution. Lloyd Weinreb makes the first significant advance toward an understanding of what rights are, how they function in our lives, and why we need them. Weinreb's central argument is that rights are tightly connected to responsibility. They are the normative constituents of persons, attributes that we have rightly, as our due. As such, they enable us to overcome the antinomy of moral freedom and natural causal order. Without them, we could not regard human beings as persons, that is, as free and responsible, or autonomous. Since responsibility is a structural feature of our experience and a matter of fact, rights too are matters of fact. Against a review of the current debates on the subject, Weinreb fully elaborates his original argument on the nature of rights and finds the source of concrete rights in the nomos, or deep conventions, of a community. Applying his theory, he shows how it helps to answer specific questions about animal rights, human rights-including, in the context of abortion and capital punishment, the right to life-and civil rights, including particularly rights of the handicapped, gay rights, and affirmative action in contemporary American society. Along the way, Weinreb shows that Oedipus and Roger Clemens have more in common than either would probably have supposed. This highly original work will significantly redirect the study of rights. It will be especially valuable to those who practice or study law, philosophy, politics, and public policy.