Germany is joining a long list of European democracies that have modified or expressed a willingness to modify their citizenship laws to denationalize first and then prevent the return of or expel those citizens accused of having participated in terrorist activities abroad. The formal labelling of citizenship deprivation as an administrative measure outside the scope of criminal justice has prevented scholars of criminal law from undertaking a thorough scrutiny of its legitimacy. In this paper I seek to fill this gap. (...) Specifically, after demonstrating why deprivation of citizenship is a measure of a criminal nature, I argue against its legitimacy, either as a punishment or as a risk-based measure. Instead I propose that we should understand citizenship deprivation as a paradigmatic response from an illegitimate enemy criminal law. Notwithstanding the foregoing, I claim that states that choose to denationalize terrorists should do it within the framework of a process with the highest (criminal procedural) guarantees. (shrink)