Customary International Law Requiring States to Grant Nationality
International Court of Justice.4 Only certain actors, primarily states, are relevant5
and their practice must be widespread and consistent.6 That being said, the practice
of international organisations can contribute to constituting a rule of customary
international law, when the organisation is acting with a competence similar to
that of states.7 In addition, this practice must be accompanied by an opinion that
the states engage in this practice under a sense of obligation.8 In order to identify
whether states have the requisite practice, we must survey a sampling of
representative states, apply inductive and deductive reasoning and conclude
whether such customary law has crystalised.9 Practice constituting customary
international law can include legislation or judicial decisions, 10 diplomatic or other
public acts, statements on policies, claims on the law11 and practice aligned with
4
5
6
7
8
9
10
11
See Statute of the International Court of Justice, art 38.
See, eg, Asylum Case (n 3) 276–77; ILC Draft Conclusions (n 3) 76 [62] conclusion 4.
See Hugh Thirlway, The Sources of International Law (Oxford University Press, 2nd edn,
2014); North Sea Continental Shelf Cases (n 3) 44.
See ILC Draft Conclusions (n 3) 76 [62] conclusion 4(2), 88–89 comments (4), (6)–(8);
Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide
(Advisory Opinion) [1951] ICJ Rep 15, 24–25; William Thomas Worster, ‘The Contribution
to Customary International Law of Territories under International Administration’ in Sufyan
Droubi and Jean d’Aspremont (eds), International Organisations, Non-State Actors and the
Formation of Customary International Law (Manchester University Press 2020) 343, arguing
that when the United Nations operates an international territorial administration, it acts
sufficiently like a state to contribute to customary international law.
See Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States
of America) (Judgment) [1986] ICJ Rep 14, 108–109 [207] (‘Nicaragua Case’); North Sea
Continental Shelf Cases (n 3) 44; Right of Passage over Indian Territory (Portugal v India)
(Judgment) [1960] ICJ Rep 6, 42–43 (‘Right of Passage Case’); Asylum Case (n 3) 276–77;
Lotus (n 3) 28; ILC Draft Conclusions (n 3) [62] conclusion 9.
See Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada v United States
of America) (Judgment) [1984] ICJ Rep 246, 299 [111] (‘Gulf of Maine Case’); Continental
Shelf (Libyan Arab Jamahiriya v Malta) (Judgment) [1985] ICJ Rep 13, [27] (‘Continental
Shelf (Libya v Malta) Case’); Nicaragua Case (n 8) 98 [185]; North Sea Continental Shelf
Cases (n 3) at 43; ILC Draft Conclusions (n 3) [62], conclusion 16(2); Jean-Marie Henckaerts
et al, ‘Introduction’ in Customary International Humanitarian Law (Cambridge University
Press 2005) vol 1, xliv, li; International Law Association, Statement of Principles Applicable
to the Formation of General Customary International Law (Final Report of the Committee
on Formation of Customary (General) International Law, 2000) 23–26, principle 14,
commentary (d)–(e) (‘ILA Statement of Principles’).
See ILC Draft Conclusions (n 3) [62] conclusions 5, 6(2); Jurisdictional Immunities of the
State (Germany v Italy) (Judgment) [2012] ICJ Rep 99, [55], [70]–[71] (‘Jurisdictional
Immunities Case’); North Sea Continental Shelf Cases (n 3) 104–106; Nottebohm Case
(Liechtenstein v Guatemala) (Judgment) [1955] ICJ Rep 4, 22; Anglo-Norwegian Fisheries
Case (United Kingdom v Norway) (Judgment) [1951] ICJ Rep 116, 134–36 (‘AngloNorwegian Fisheries Case’); Prosecutor v Furundžjia (Judgment) (International Criminal
Tribunal for the Former Yugoslavia, Trial Chamber, Case No IT-95-17/1-T, 10 December
1998) [168] (‘Furundžjia Trial Judgment’); ILA Statement of Principles (n 9) 18, principle 9
commentary (c).
See Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep
226, 257 [86]–[88] (‘Nuclear Weapons Advisory Opinion’); Continental Shelf (Tunisia v
Libyan Arab Jamahiriya) (Judgment) [1982] ICJ Rep 38, [24]; Gabčikov-Nagymaros Project
(Hungary v Slovakia) (Judgment) [1997] ICJ 7, 39–42 [49]–[54] (‘Gabčíkovo-Nagymaros
Case’); Nicaragua Case (n 8) 97–109 [183]–[207]; North Sea Continental Shelf Cases (n 3)
24–25 [25]–[26], 26–27 [32]–[33]; Fisheries Jurisdiction Case (United Kingdom of Great
Britain and Northern Ireland v Iceland; Germany v Iceland) [1974] ICJ Rep 3, 24–26
(‘Fisheries Jurisdiction Case’); Gulf of Maine Case (n 9) 270 [34]; Lotus (n 3) 23, 26–30;
ILC Draft Conclusions (n 3) [62] conclusions 6(2), 10(2), 19(2); ILA Statement of Principles
(n 9) 14–15 principle 4 commentary (a), principle 40–41 principle 19 commentary (a).
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