“Foreign”, “Terrorist”, “Fighter”? The fundamental principle of legality and certainty in the law is put under strain by terms that are vague and uncertain in scope. While particularly stringent requirements arise in relation to nullum crimen sine lege (no crime without law) or nulla poena sine lege (no punishment without law),65 considered in section 3.3 on criminal law, all restrictions on rights (such as permissible limitations on freedom of expression, association or private life) must be clearly provided for in law. Multiple human rights issues arise from the use of the term “foreign terrorist fighters”, leading several initiatives to call for reconsideration of the approach to the definition of “foreign terrorist fighters”, given the dangers inherent in the scope of the label. Each element of the term has given rise to controversy and uncertainty: • UNSC Resolution 2178 (2014) associates the term “foreigner” with individuals who “travel to a State other than their States of residence or nationality”. However, the term still leaves significant margin of ambiguity. In line with basic principles of international law, dual nationals or persons with important personal, social, cultural and family links to states, beyond formal residence or nationality, should not be considered “foreigners” for this purpose when they travel to the state with which they have the relevant links.66 • The fact that there is no internationally agreed definition of the term “terrorist” or “terrorism” leaves significant space for diverse and far-reaching interpretations by national authorities, and increases the potential for abuse when implementing UNSC Resolution 2178.67 Human rights courts and bodies have frequently criticized broad and ambiguous definitions of terrorism as being in violation of the principle of legality and of other rights.68 The concerns are compounded in the FTF context by an accumulation of additional ambiguous related concepts. • Provisions on “foreign terrorist fighters” commonly cover travel to support “terrorist organizations” and entities, but the question of how that qualification is made, and by whom, is not addressed. It does not appear to be limited to travelling to join or support groups specifically designated or listed as “terrorist”’ by the UN or regional groupings such as the EU. Arguably, confining the term in this way would at least limit the scope for abuse, though it would not eradicate it entirely, as the listings processes 65  Article 15 of the International Covenant on Civil and Political Rights (ICCPR); Article 7 of the European Convention on Human Rights (ECHR). 66  UNSC Resolution 2178 (2014) refers in para. 6 to prosecuting travel to states other than states of residence or nationality, op. cit., note 1. See fuller discussion of possible ambiguities in S. Krähenmann, “The Obligations under International Law of the Foreign Fighter’s State of Nationality or Habitual Residence, State of Transit and State of Destination” in FFILB (2016), p. 235, op. cit., note 14. 67  See criticism by M. Scheinin, “Back to post-9/11”, op. cit., note 51. 68  For examples, see: H. Duffy, The ‘War on Terror’ and the Framework of International Law, Second Edition (Cambridge: Cambridge University Press, 2015), Chapter 7B. 22 Guidelines for Addressing the Threats and Challenges of “Foreign Terrorist Fighters”