C. Paulussen country of origin or their country of habitual residence to join a party engaged in an armed conflict”, most notably the conflict in Syria and Iraq. After that, the article will focus on considerations in the context of international humanitarian law, which have been less frequently the subject of academic debate. This contribution concludes that citizenship stripping is not only highly problematic under international human rights law, but also from the perspective of international humanitarian law. The measure – which is likely to constitute cruel, inhuman or degrading treatment or punishment – violates Article 3 Common to the four Geneva Conventions, but it also undermines accountability for international humanitarian law violations already committed and can engender new violations through the non-removal of the suspect from the conflict zone. One of the few positive sides of the connection between the measure and international humanitarian law is that even if nationality is deprived, this will not have an effect on the international humanitarian law obligation to treat that deprived person humanely. In that sense, international humanitarian law provides a welcome – albeit temporary – safety net of decent treatment for people who have become victims of countries’ refusal to take responsibility for their own citizens. Keywords: citizenship stripping, deprivation of nationality, foreign fighters, international humanitarian law, international human rights law. Introduction Various armed conflicts around the world have attracted foreign fighters, who have been defined as “individuals, driven mainly by ideology, religion and/or kinship, who leave their country of origin or their country of habitual residence to join a party engaged in an armed conflict”.1 Examples are the British national George Orwell, who participated in the Spanish civil war in the 1930s on the side of the republicans, the Saudi national Osama bin Laden, who arrived in Afghanistan in 1 A. de Guttry, F. Capone and C. Paulussen, “Introduction”, in A. de Guttry, F. Capone and C. Paulussen (eds), Foreign Fighters under International Law and Beyond, Asser Press/Springer: The Hague 2016, p. 2. This definition (and hence also this article) excludes mercenaries, as the latter are motivated to take part in the hostilities essentially by the desire for private gain. See also S. Krähenmann, Foreign Fighters under International Law, Academy Briefing No. 7, Geneva Academy of International Humanitarian Law and Human Rights, Geneva, October 2014, p. 16. However, for a different opinion, see UN General Assembly, Use of Mercenaries as a Means of Violating Human Rights and Impeding the Exercise of the Right of Peoples to Self-determination: Note by the Secretariat, A/73/303, United Nations, New York, 6 August 2018, para. 9: “In the absence of either an internationally agreed legal definition of foreign fighters or a specific regime governing them, the Working Group has defined foreign fighters as individuals who leave their country of origin or habitual residence and become involved in violence as part of an insurgency or non-State armed group in an armed conflict. They are motivated by a range of factors, notably ideology, although the Working Group has found financial motivations to be a key factor as well. In this regard, the Working Group deems foreign fighters as a mercenary-related activity [original footnote omitted].” For more information on the status of foreign fighters under international humanitarian law more generally, see E. Sommario, “The Status of Foreign Fighters under International Humanitarian Law”, in A. de Guttry, F. Capone and C. Paulussen (eds), above, pp. 141–160. 606