This chapter, a contribution to a book on International Legal Positivism in a Post-Modern World, gauges the potential for mutually enriching interactions between international legal positivism and legal realism. It first describes the encounter between legal positivism and legal realism in the U.S. legal academy and then proceeds to discuss the rise of a new legal realism in international legal theory. In a concluding section, the chapter assesses the compatibilities and tensions between the new international legal realism and the new international legal positivism.With its forthright embrace of the inescapability of uncertainty in law, the new international legal positivism adopts a sceptical position very similar to legal realism. However...