This book presents a detailed empirical account of the evolution of EU counterterrorism policy between 2001 and 2005, dating from 9/11 to the 7/7 attacks. The volume provides a thorough theoretical exploration of the 'windows of opportunity' in EU security policy after 9/11. It is not sufficient to refer simply to the 'shock' of terrorist attacks to explain periods of intensive EU policy-making. Rather, the author develops an innovative theoretical framework on the basis of the multiple streams framework from US public policy analysis. This framework specifies how policy entrepreneurs rely on a number of contextual factors in their promotion of non-incremental agenda- and policy-change. In addition, the theory of actor-centred institutionalism is used to portray the contrast between policy-making during and after windows of opportunity. Overall, the book shows why the EU's counter-terrorism agenda could expand in a very dynamic fashion, but has also been highly inconsistent across different policy areas and beset by implementation problems. This fits into wider debates on the EU's fight against terrorism. On the one hand, the EU has avoided the excesses of the US 'War on Terror', which could also be seen as the expression of a more experienced 'European culture of counterterrorism'. On the other hand, the EU has little to show by way of transformative or innovative policies that could undercut the political or ideological appeal of terrorist groups. Instead, the EU decision-making system has increasingly locked-in over-technocratic approaches to security provision. Finally, the detailed historical analysis can serve as a baseline for assessing the impact of the Lisbon Treaty in this issue area. This book will be of much interest to students of EU policy, Counter-Terrorism, European Security, public administration, foreign policy and IR in general.