A significant part of Kelsen’s work is devoted to the theoretical and methodological separation of positive law from natural law. The predominant impression of this process is of a determination to entirely sunder the conceptual framework of positive law from any continuing reliance upon natural law. However, certain of Kelsen’s works involve the appropriation of the notion of civitas maxima from Christian Wolff’s Jus Gentium Methodo Scientifica Pertractatum (1749). The presence of this notion raises the question of the relationship between Kelsen’s theoretical framework and the conception of natural law developed by Christian Wolff. It is through an examination of the transformation of Wolff’s notion of civitas maxima that an important aspect of Kelsen’s relationship to the natural law tradition becomes apparent. The appropriation will be traced through the initial discussion of civitas maxima in Kelsen’s Das Problem der Souveränität und die Theorie des Völkerrechts. Beitrag Zu Einer Reinen Rechtslehre (1920/1928), and its further exposition and development in Kelsen’s 1926 Lecture Course (‘Les Rapports de Système entre le Droit Interne et le Droit International’) at the l’Académie de droit international, in the Hague. In this manner, the significant methodological divergences between a Kelsenian theory of positive law, as a theory of legal monism according primacy to international law, and the Wolffian theory of natural law, as a theory of the law of nations, will become evident. This methodological divergence, however, should not obscure a more than residual affinity between Kelsen and Wolff concerning the cosmopolitical orientation of their thought.