After the attacks of 9/11, 2001 terrorism and other forms of transnational risks of violence dominated official security policy. Researchers at the Institute for Peace Research and Security Policy at the University of Hamburg investigated the consequences this change for security governance in a multi-annual research program. Case studies of particular issue areas of transnational risks of violence show that security policies changed but that national governments remained dominant. The transnationalisation of threat perceptions only led to a limited internationalisaton of security policies. The volume presents results of the research program. It combines conceptual work on security governance with empirical research, for instance on counterterrorism, changing perceptions of security in international organizations, such as the European Union and the Organization for Security and Co-operation in Europe. With contributions by Raphael Bossong, Hans-Georg Ehrhart, Hendrik Hegemann, Regina Heller, Margret Johannsen, Roland Kaestner Martin Kahl, Anna Kreikemeyer, Oliver Meier, Kerstin Petretto, Daniela Pisoiu, Johann Schmid, Patricia Schneider Arne C. Seifert, Matenia Sirseloudi, Eric van Um und Wolfgang Zellner