The argument is that the philosophy of natural law and contemporary theories about the nature of justice are both efforts to make sense of the fundamental paradox of the human experiences of individual freedom and responsibility in a causally determined universe. The natural law tradition is traced from its origins in Greek speculation through its classic Christian statement by Thomas Aquinas. How the social contract theorists adapted the idea of natural law to provide for political obligation in civil society is shown, as well as how the idea was transformed in Kant's account of human freedom. The historical narrative is brought to the present with a discussion of the contemporary debate between natural law and legal positivism, including particularly the natural law theories of Finnis, Richards, and Dworkin. The approach of modern political philosophy is then adopted to develop the idea of justice as a union of the distinct ideas of desert and entitlement. Liberty and equality are shown to be the political analogues of desert and entitlement and both pairs to be the normative equivalents of freedom and cause. The theories of justice of Rawls and Nozick as well as the communitarian theory of MacIntyre and Sandel are considered. The conclusion unifies the debates about natural law and justice as parallel efforts to better understand the human condition. Notes and index.