The act of violence of 9/11 changed the global security agenda, catapulting terrorism to the top of the agenda. Weapons of mass destruction grabbed public interest and controlling the free movement of people became a national security priority. In this volume, Jef Huysmans critically engages with theoretical developments in international relations and security studies to develop a conceptual framework for studying security. He argues that security policies and responses do not appear out of the blue, but are part of a continuous and gradual process, pre-structured by previous developments. He examines this process of securitization and explores how an issue, on the basis of the distribution and administration of fear, becomes a security policy. Huysmans then applies this theory to provide a detailed analysis of migration, asylum and refuge in the European Union.