Chapter Five moves back in time and from theory to application, revealing the potential and the limitations of natural law theory in an actual political setting. It analyzes the political rhetoric of Tertullian, the Carthaginian Christian theologian who argued, against Roman policy, for universal religious freedom, using the term libertas religionis perhaps for the first time on record. This chapter provides a fresh reading of Tertullian’s writings as they concern religious freedom and related themes, drawing attention to his reliance on natural law argumentation. I analyze his epistemological commitments and link them to the commitments of the use of natural law by the other writers in the book. Finally, I argue that the effectiveness of Tertullian’s argument for universal religious freedom relied heavily on his use of natural law as a mediating device between human and divine law, with implications for the utility of natural law reasoning in a pluralistic public sphere.