Ever since the terrorist attacks in New York, Madrid and London issues of security have constantly been on the agenda of states and transnational organizations alike. While on the one hand aimed at protecting a society, security measures on the other hand also tend to challenge its core constitutional values like democracy, fundamental rights and the rule of law. The proceedings at hand combine contributions of various academics and practitioners in the field of security research. Apart from analysing the impact of security politics on recent developments of international, European and national constitutional law, the authors also provide ideas on how to limit security within today’s constitutional design.