In view of the Paris Climate Conference in December 2015, where the adoption of a universal, binding climate agreement is foreseen, this note examines the respective roles of the European Union (EU) and the United States (US) in shaping the international response to climate change, and considers the prospects for the adoption and implementation of such a new climate agreement. It considers how the EU and the US have contributed to the design and implementation of the relevant international legal norms, addressing the shift in leadership from the US to the EU in the 1990s, EU activism through the Emission Trading Scheme (ETS) and ambitious emission reductions, and the renewed commitment from the Obama Administration since 2013, including US-China cooperation. This article discusses the EU and US perspectives on the adoption and implementation of a new climate agreement, focusing on its legally binding nature. The author concludes that an adequate system of monitoring and verification mechanisms at the domestic and international levels is a conditio sine qua non for any new climate agreement. A system of “checks and balances”, limiting the role of international law to one offacilitation, rather than prescription, may be the first step towards an innovative and more effective normative framework.