PRIO has organized an international conference on the costs of security and the value of liberty in an age of trans-national terrorism. Around 80 people took part in the conference. Organized by COST Action 24 The Evolving Social Construction of Threat, the Sixth Framework Programme Integrated Project The Changing Landscape of Security and Liberty in Europe (CHALLENGE), and the PRIO Strategic Institute Programme The Threat to Europe funded by the Research Council of Norway. Questions and queries: J. Peter Burgess