This chapter outlines the emergence and explains the rationale of the European Union's strategies and polices aimed at preventing nuclear proliferation to states and terrorists. It charts briefly the EU's response to the illicit trade in nuclear materials in the 1990s, which already raised concerns about terrorist access to such materials, and contrasts this with the US approach. It then shows where and explains why the EU has since made substantial progress in defining and implementing a non-proliferation strategy which focuses on the control and containment of nuclear material, technology and know-how. The rise of global terrorism and the transatlantic rift over Iraq are identified as key stimuli for the EU's formulation of two central documents: the European Security Strategy and WMD Non-Proliferation Strategy. At the core of both is the EU's emphasis on strengthening multilateral approaches to security. The chapter shows how this is translated into the EU's nuclear non-proliferation policies and discusses where the EU has a credibility problem. The final part of the chapter suggests which lessons learnt from the Libyan experience might be applied in EU (and US) approaches to Iran.