In the twenty-first century, the European Union is confronted by myriad security problems that demand concerted action and cooperation. As a negotiating power, it seeks to persuade Iran to forswear a nuclear weapons programme. As a crisis manager it seeks to contribute to global peace and stability through civilian and military operations. Closer to home, it is wrestling with questions about membership enlargement, large-scale migration and terrorist threats to the security of its populations and infrastructure. European governments, already under financial strain from ageing workforces and welfare systems, face ever more difficult choices about budget cuts in security and defence after the near-collapse of the global banking system. Will it be possible to enhance cooperation between member states? How can the EU complete its transition from a security actor with great potential to a player that credibly aligns available policy instruments and resources?These and other issues about the very nature and identity of the Union are explored in this Adelphi. From the need to establish its hard-power credentials, overcome its reluctance to demonstrate them against non-compliant states, and leverage its relationships with other great powers, to attempts to break its dependence on Russian energy, it is clear the EU has its work cut out. But, by affirming its commitment to multilateralism and defining a careful balance between closer cooperation and the national security concerns of EU member states, this book suggests, the European Union can build on its status as a global security power in the making.