Academic discourse on global justice is at an all-time high. Within ethics and international law, scholars are undertaking new inquiries into age-old questions of building a just world order. Ethics – within political and moral philosophy – poses fundamental questions about responsibilities at the global level and produces a tightly reasoned set of frameworks regarding world order. International law, with its focus on legal norms and institutional arrangements, provides a path, as well as illuminates the obstacles, to implementing theories of the right or of the good. Yet despite the complementarity of these two projects, neither is drawing what it should from the other. The result is ethical scholarship that often avoids, or even misinterprets, the law; and law that marginalizes ethics even as it recognizes the importance of justice. The cost of this avoidance is a set of missed opportunities for both fields. This article seeks to help transform the limited dialogue between philosophers and international lawyers into a meaningful collaboration. Through a critical stocktaking of the contributions of the two disciplines, examining where they do and do not engage with the other, it offers an appraisal of the causes and costs of separation and an argument for an interdisciplinary approach.