This book contributes to the understanding of the counter-terrorism (CT) policy of the European Union (EU) by offering a set of analyses focusing on its external dimension. Whilst calling for the combination of internal and external policies as well as cooperation with third countries and international institutions, the external dimension of EUCT challenges previous assumptions on the functioning of the EU and offers new testing ground for the latest theoretical and methodological approaches. This volume provides the first systematic assessment of the external dimension of EUCT. It covers transatlantic counter-terrorism cooperation, the interaction between EU institutions and policies, theoretical debates on EU actorness in counter-terrorism and the role of judicial institutions in international counter-terrorism. Furthermore, it draws attention to the need for engaging in new discussions over the post-Lisbon Treaty Common Foreign and Security Policy (CFSP), the international fight against terrorism, and the way international actors cooperate and compete on the security arena. It will be of interest for both academics and practitioners working on EU foreign policy, transatlantic relations and international counter-terrorism. It will also be of interest for students and journalists specialized on European and international affairs. This book was published as a special issue of European Security.