This chapter draws on an analytical framework centered on the theoretical notion of actorness as well as the political concept of effective multilateralism. It outlines the European Union's (EU) contribution to the special negotiation format that, next to the France, Germany, and the United Kingdom (E3)/EU, also included China, Russia, and the United States, and worked in close cooperation with the International Atomic Energy Agency and the UN Security Council. The chapter provides an outlook on how Europe, together with its transatlantic partner, could – and should – not only implement the deal itself but also broaden its reach with regard to both regional cooperation and strengthening the global nonproliferation regime. It summarizes the EU's role on this issue, building on an assessment of its actorness. The chapter highlights the EU's ambition to engage Iran based on the EU's core concept of effective multilateralism.