Deprivation of national citizenship is one of the strategies used to counter the phenomenon of foreign terrorist fighters, that is, individuals traveling abroad for the purpose of terrorism. This Article begins with a short overview of the case-law of the European Court of Human Rights on the deprivation of citizenship. In these cases, the contestation of the deprivation of citizenship was based on the infringement of the rights to private and family life. We then turn to the limits imposed by EU law on decisions made by national authorities of Member States concerning citizenship deprivation of foreign terrorist fighters. Focusing on recent cases of the Court of Justice of the European Union (CJEU) concerning the European citizenship, we address the evolving role that EU law plays in the assessment of the proportionality of Member States’ decisions to strip individuals of national citizenship. We also consider the national practice, focusing on a recent decision in Denmark. In addition, we consider legal issues arising from the repatriation of Foreign Terrorist Fighters and their children. We argue that EU citizenship thus offers a further layer of protection against the deprivation of citizenship and that Member States are under a positive obligation to repatriate EU citizens who are the children of Foreign Terrorist Fighters on account of the case-law stemming from the Ruiz-Zambrano and X (Thai national) cases. For the moment, no common approach to repatriation of foreign fighters, or their children, is taken by EU member States in the context of the EU.