Over the past decade, it has become commonplace to contrast the positions of the United States and the European Union toward the rule of international law, with the US being characterized at best by ambivalence, and at worst as a “rogue nation.” The EU, by contrast, has been seen as a strong supporter of international law. This symposium interrogates this conventional wisdom, formulating and testing a theoretical framework that attempts to disaggregate both the nature and the causes of support for international law. This article is organized in five sections. Section 1 introduces the aims of the symposium and the basic elements of its theoretical framework. Section 2 problematizes the dependent variable, “support” for international law, disaggregating that concept into four discrete dimensions of leadership, consent, compliance, and internalization. Section 3 identifies four sets of independent variables—international and domestic, political and legal—that might account for observed US–EU differences. Section 4 introduces the five empirical papers in the symposium, which deal with human rights law, criminal law, environmental law, trade law, and the internalization of international law by domestic courts. Section 5 concludes with preliminary findings. With respect to the dependent variable, we find considerable differences between the US and the EU, but we also identify important nuances in the nature of those differences, which center primarily around the dimensions of consent and internalization. In terms of the independent variables, we find that the roots of US and EU differences are complex and multi-causal, defying any effort to reduce those differences to simple contrasts such as American exceptionalism or the EU’s normative difference.