1 E.g., H. Schermers, ‘The Legal Bases of International Organization Action’, in R. Dupuy (ed.), A Handbook on International Organizations (1998), 401, at 402; P. Sands and P. Klein (eds.), Bowett’s Law of International Institutions (2009), 463–4; C. F. Amerasinghe, Principles of the Institutional Law of International Organizations (2005), 386–7; A. Reinisch, ‘Sources of International Organizations’ Law: Why Custom and General Principles are Crucial’, in S. Besson and J. D’Aspremont (eds.), The Oxford Handbook of the Sources of International Law (2017); Daugirdas, K., ‘How and Why International Law Binds International Organizations’, (2016) 57 Harvard International Law Journal 325 Google Scholar; and, taking a more cautious approach, J. Klabbers, ‘Sources of International Organizations’ Law: Reflections on Accountability’, in J. d’Aspremont and S. Besson, The Oxford Handbook on the Sources of International Law (2017), 998–9. Support for the proposition that international organizations are bound by general international law is found in Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt (Advisory Opinion) [1980] ICJ Rep. 73, at 89–90 and Prosecutor v. Rwamakuba, Case No. ICTR-98-44C-T, Decision on Appropriate Remedy (2007), para. 48. I investigate this issue in F. L. Bordin, The Analogy between States and International Organizations (2018), 13–85.

2 I shall use the phrase ‘general international law’, found, e.g., in Art. 53 VCLT 1969, in the sense that it has been used in the case law of the ICJ and in the work of the ILC, that is, to describe default rules of general application to be distinguished from special rules agreed between specific parties (lex specialis): see, e.g., Conclusions of the Work of the Study Group on the Fragmentation of International Law, YILC 2006/II, Part Two, 179, and Accordance with International Law of the Unilateral Declaration of Independence in Respect of Kosovo, Advisory Opinion of 22 July 2010, [2010] ICJ Rep. 403, at 436–9, paras. 79–84. In the scheme of sources found in Art. 38(1) of the ICJ Statute, that would comprise customary international law (including rules achieving the status of jus cogens) and general principles of law. The phrase has not always been used consistently: in Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, for example, the ICJ has used the puzzling variation ‘general rules of international law’, which a prominent commentator has understood to refer to ‘secondary rules’ of international law only: Klabbers, supra note 1, 998–9. Despite this inconsistency in usage, the phrase is favoured over ‘customary international law’ for its inclusivity: it encapsulates norms of general application without taking a position as to how they are formed or identified.

3 Art. 2(d) ARIO defines ‘rules of the organization’ as ‘the constituent instruments, decisions, resolutions and other acts of the international organization adopted in accordance with those instruments, and established prac-tice of the organization’; cf. also the slightly different formulation in Art. 2(i)(j) VCLT 1986. I shall use the phrase interchangeably with ‘internal law’ or ‘internal rules’ of IOs.

4 The ILC made this distinction when it considered the applicability of the regime of countermeasures to IOs. In his Eighth Report, Gaja invited the Commission to consider the difference between ‘on the one hand, non-compliance by a State with its obligations as a member of the organization and, on the other, non-compliance with obligations that the member State may have otherwise acquired’: A/CN.4/640 (2011), at. 23, para 66. Also, Wood, A/CN.4/SR.3084 (2011), at 5.

5 The Reparation for Injuries advisory opinion is a case in point. The ICJ failed to distinguish between the question of general international law of whether the UN had the capacity qua international legal subject to bring claims on the international plane and the question of UN law of whether it had been given the competence to exercise that capacity under the UN Charter. That makes its reasoning both misleading and confusing. See Reparation for Injuries Suffered in the Service of the United Nations, Advisory Opinion of 11 April 1949, [1949] ICJ Rep. 174, at 177–80.

6 Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, supra note 1, at 92.

7 Reparation for Injuries Suffered in the Service of the United Nations, supra note 5, at 179. Though the Court’s analysis of the character of the 1946 Convention is persuasive, it should be noted that the example that it chose is somewhat misleading: the UN is the beneficiary, but not itself a party, to the 1949 Convention.

8 Art. 2(1)(a) VCLT 1986.

9 Commentary to Art. 2, Yearbook of the International Law Commission (hereinafter YILC) 1982/II, Part One, at 18, para. 4.

10 Reuter (Third Report), YILC 1974/II, Part One, at 140, para. 6. Reuter had initially proposed to define a ‘treaty concluded between States and international organizations or between two or more international organizations’ as an agreement governed ‘principally’ by ‘general’ international law.

11 Cf. Art. 34 of VCLT 1969: ‘A treaty does not create either obligations or rights for a third State without its consent’.

12 Commentary to Art. 32, YILC 2011/II, Part Two, at 78, para. 3.

13 Ahlborn, C., ‘The Rules of International Organizations and the Law of International Responsibility’, (2012) 8 IOLR 397 Google Scholar, at 471–2.

14 Conclusions of the Work of the Study Group on the Fragmentation of International Law, supra note 2, para. 5.

15 Ibid.

16 S. Rosenne, Developments in the Law of Treaties 1945-1986 (1989), 257.

17 The commentary to the provision ultimately adopted as Art. 5 VCLT 1969 explains that the phrase ‘adopted within an international organization’ was ‘intended to exclude treaties merely drawn up under the auspices of an organization or through use of its facilities and to confine the reservation to treaties the text of which is drawn up and adopted within an organ of the organization’: YILC 1966/II, 191, para. 3.

18 Commentary to Art. 27, YILC 1982/II, Part Two, at 38–9, para. 4. This was also the opinion of Roberto Ago, then rapporteur on state responsibility: YILC 1977/I, at 110–11, para. 14. The commentary adds that under the law of responsibility an IO could ‘deny a contracting State the benefit of the performance of a treaty if that State has committed a wrongful act against the organization’, including ‘a breach of the rules of the organization if the State is also a member of the organization’ (para. 4, emphasis in original). In this odd passage, the Commission appears to be referring to countermeasures.

19 Reuter, YILC 1981/I, at 167, para. 24.

20 Reuter, YILC 1979/I, at 94–5, para. 28.

21 Ibid. In an essay on the Vienna Conference, Reuter reiterated that the relations between organizations and members ‘sont régies par un système juridique individualisé pour chaque organisation’: P. Reuter, ‘La Conférence de Vienne sur le Droit des Traités entre Etats et Organisations Internationales ou entre Organisations Internationales’, in F. Capotorti et al. (eds.), Du Droit International au Droit de l’Intégration (1987), 563–4.

22 Commentary to Art. 46, YILC 1982/II, Part Two, at 52, para. 8.

23 Conclusions of the Work of the Study Group, supra note 2, conclusions 4 and 6.

24 Commentary to Art. 64, YILC 2011/II, Part Two, at 102, para. 1: ‘Special rules relating to international responsibility may supplement more general rules or may replace them, in whole or in part. These special rules may concern the relations that certain categories of international organizations or one specific international organization have with some or all States or other international organizations.’

25 Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, supra note 1, at 93.

26 Ibid., at 158 (Judge Ago, Separate Opinion). It should be noted that the Court does not provide a clear explanation of the source of the ‘mutual obligations of co-operation and good faith’, rather making a blank reference to ‘general international law … the Constitution of the Organization … and the agreements in force between Egypt and the Organization’ (para. 48). An argument could be made that the obligations of co-operation and good faith derive ipso jure from the rules of the organization, in which case the latter would be the source of the obligation, applicable as lex specialis, as opposed to a special customary rule addressed at organizations and members.

27 Commentary to Art. 52, YILC 2011/II, Part Two, at 93, para. 2.

28 It should be noted that Art. 51(4) is meant to apply to all countermeasures, even those that third parties may take against international organizations. Why the performance of the organization’s functions should be of any concern to non-members – which surely are under no special obligations of mutual co-operation and good faith – is unclear.

29 The expression is borrowed from Ahlborn, supra note 13, at 450.

30 Nuclear Tests (Australia v. France) (Judgment) [1974] ICJ Rep. 253, at 286.

31 The Court notes, at para. 48, that its ‘essential task’ was to ‘determine the specific legal implications of the mutual obligations incumbent upon Egypt and the Organization in the event of either of them wishing to have the Regional Office transferred from Egypt’.

32 Interpretation of the Agreement of 25 March 1951 between the WHO and Egypt, supra note 1, paras. 45–7.

33 YILC 2002/II, Part Two, at 93, para. 467.

34 Ibid.

35 Commentary to Art. 10, YILC 2011/II, Part Two, at 64, para. 7.

36 Ibid.

37 Ibid.

38 Ibid.

39 In the commentary, the Commission refers to the school of thought that draws ‘a distinction according to the source and subject matter of the rules of the organization, and exclude, for instance, certain administrative regulations from the domain of international law’ (ibid., at 63, para. 5).

40 As Pellet pointed out, the rules of the organization are ‘anchored in general international law’: YILC 2003/I, at 27, para 51. Balladore Pallieri has argued, on the grounds that a constituent instrument is ‘un acte international, régit par les normes générales du droit international ou par des norms particulières existant à ce sujet dans le droit international’, that there is no such a thing as the ‘internal law’ of IOs. His convoluted analysis conflates the question of the character of the rules of the organization with the question of whether general international law applies to IOs: Balladore Pallieri, G., ‘Le Droit Interne des Organisations Internationales’, (1969) 127 RCADI 1 Google Scholar, at 16–17.

41 Legality of the Use of Nuclear Weapons in Armed Conflict, Advisory Opinion of 8 July 1996, [1996] ICJ Rep. 66, at 74, para. 19.

42 Ibid. For a recent discussion of the dual character of constituent instruments see Gabarri, L., ‘The Dual Legality of the Rules of International Organizations’, (2017) 4 IOLR 87 Google Scholar.

43 Ahlborn, supra note 13, at 413. In the words of the ICJ, constituent instruments are ‘treaties of a particular type’ that ‘create new subjects of law endowed with a certain autonomy, to which the parties entrust the task of realizing common goals’: Legality of the Use of Nuclear Weapons in Armed Conflict, supra note 41, at 74, para. 19.

44 Appeal Relating to the Jurisdiction of the ICAO Council (India v. Pakistan), Judgment of 18 August 1972, [1972] ICJ Rep. 46, at 130 (Judge De Castro, Separate Opinion).

45 H. Kelsen, General Theory of Law and State (1945), at 99–100. See also Facsaneanu, L., ‘Le Droit Interne de l’Organisation des Nations Unies’, (1957) III Annuaire Français de Droit International 315 CrossRefGoogle Scholar, at 319–20, 324–5 (refering to la théorie de l’institution developed by German private lawyers which points to the ‘aptitude’ of all organized – or, more precisely, personified – communities to establish their own autonomous legal system); G. Hartmann, ‘The Capacity of International Organizations to Conclude Treaties’, in K. Zemanek (ed.), Agreements of International Organizations and the Vienna Convention on the Law of Treaties (1971), at 150. In contrast, while viewing the ‘internal law’ of IOs as an autonomous legal order, Cahier observes that ‘[l]a personnalité juridique apparaît donc dans ce domaine comme sans importance’: Cahier, P., ‘Le Droit Interne des Organisations Internationales’, (1963) 67 RGDIP 563 Google Scholar, at 574; that makes his argument weaker: the sense in which the rules of the organization can claim to be autonomous from international law is the same sense in which the by-laws of a juristic person can claim to be autonomous from the domestic law of states.

46 Ahlborn, supra note 13, at 413.

47 Ibid.

48 Facsaneanu, supra note 45, at 326.

49 Ibid.

50 As Kelsen explains, the ‘[t]he relation between the total legal order constituting the State, the so-called law of the State or national legal order, and the juristic person of a corporation is the relation between two legal orders, a total and a partial legal order, between the law of the State and the by-laws of the corporation’: General Theory, supra note 45, at 100. For Kelsen, it should be clarified, the same logic applies to the juristic person of the state: ‘the State too is a corporation’, with ‘external obligations and rights … stipulated by the international, internal ones by the national legal order’: Pure Theory of Law (1967), 290. His work does not deal with international organizations, but the analysis is no doubt apposite. See also G. Arangio-Ruiz, ‘International law and Interindividual Law’, in J. Nijman and A. Nollkaemper (eds.), New Perspectives on the Divide between National and International Law (2007), 17 at 42–3 (pointing to a ‘high degree of similarity between the relationship of international organs’ legal orders to international law and the relationship of national legal systems to international law’). At the ILC, see Koskenniemi, YILC 2005/I, at 78, para. 34.

51 Cf. Art. 27 VCLT 1969 and Art. 3(2) ARS.

52 The point is clearly stated in A. Cassese, International Law (2005), 219.

53 Unless, of course, an international obligation specifically requires the adoption of legislation, as is the case with Art. 2, 1969 American Convention on Human Rights and Art. 4, 1984 Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment.

54 In the words of the PCIJ, ‘[f]rom the standpoint of International Law and the Court which is its organ, national laws are merely facts which express the will and constitute the activities of States’: Certain German Interests in Polish Upper Silesia, PCIJ Rep Series A No 7, at 19.

55 The mainstream position is that the debate between monism – the view of international and municipal law constituting one legal system – and dualism – the view of international and municipal law constituting two distinct legal systems – is otherwise fruitless and often fails to make sense of the practice of national courts: e.g., J. Crawford (ed.), Brownlie’s Principles of Public International Law (2012), 50.

56 As recognized, in the context of IOs, by Art. 64 ARIO on lex specialis.

57 Cf. Arts. 53 and 64 VCLT 1969. On the invalidity of decisions of IOs that are in breach of peremptory norms see A. Orakhelashvili, Peremptory Norms in International Law (2006), 465–9.

58 For commentary see O. Murray, ‘Piercing the Corporate Veil: The Responsibility of Member States of an International Organization’, (2011) IOLR 291.

59 See, e.g., Conclusions of the Work of the Study Group, supra note 2, at 180, para. 16.

60 A separate question, which is beyond the scope of this study, is how treaties are incorporated into the internal law of IOs.

61 For example, this is the established position, whether via constitutional provisions or court decisions, in the United Kingdom, the United States, Germany, Italy, and Russia: Crawford, supra note 55, 67–71, 80–2, 88–93.

62 See, e.g., O’Keefe’s discussion of the paucity of examples of meaningful application of custom by courts in the United Kingdom: ‘The Doctrine of Incorporation Revisited’, (2008) 79 BYIL 7, 23–44. See also Sales, P. and Clemens, J., ‘International Law in Domestic Courts: The Developing Framework’, (2008) 124 Law Quarterly Review 388 Google Scholar, at 415–16.

63 See Feldman, D., ‘Monism, Dualism and Constitutional Legitimacy’, (1999) 20 Australian Year Book of International Law 105 CrossRefGoogle Scholar, at 106–7. Also Sales and Clemens, supra note 62, at 389–94.

64 Gaja, YILC 2005/I, at 64, para. 55.

65 Triepel, H., ‘Les Rapport entre le Droit Interne et le Droit International’, (1923) 1 RCADI 77 Google Scholar, at 80–91.

66 In Walz v. Clickair SA, for example, the Court of Justice of the EU referred to the concept of injury enshrined in Art. 31(2) ARS as ‘common to all the international law sub-systems’ and expressing ‘the ordinary meaning to be given to the concept of damage in international law’: Case C-63/09, Walz v. Clickair SA [2010] ECR I-4239, para. 27.

67 Conclusions of the Work of the Study Group, supra note 2, paras. 11–12.

68 Ibid., para. 11.

69 The focus of the ILC was on specialized treaty regimes, especially the European system of human rights and the WTO. While the WTO is an IO, it is peculiar in that it mostly serves as a forum for the adoption of trade-related regulation by states and as a mechanism for dispute settlement. Thus, the ILC study did not specifically look into the role of general law in the relations between the WTO and its members on the institutional plane.

70 Conclusions of the Work of the Study Group, supra note 2, at 178, para. 14.

71 Ibid., at 179, para. 15.

72 Ibid at 180, para. 16.

73 Koskenniemi (Rapporteur), ‘Report of the Study Group of the ILC: Fragmentation of International Law’, A/CN.4/L.682 (2006) 93, para. 176.

74 Ibid., at 93–4, para. 177.

75 Ibid., at 96–7, para. 185.

76 J. Pauwelyn, Conflict of Norms in Public International Law: How WTO Law Relates to other Rules of International Law (2003), 37. Similarly, Simma and Pulkowski have argued that ‘general international law provides a systemic fabric from which no special regime is completely decoupled’, and that ‘by framing a prescription in legal terms, states have opted to subordinate a particular issue to the logic of international law as a whole’: B. Simma and D. Pulkowski, ‘Of Planets and the Universe: Self-Contained Regimes in International Law’, (2006) 17 EJIL 483, at 529.

77 Koskenniemi, YILC 2005/I, at 78–9, para. 34. He added that ‘[m]ost of the major international organizations had special rules to deal with a breach of an internal rule, and it was clear that such rules ought to take precedence over the general rules that the Commission was drafting, but that certainly did not mean that general law was set aside’.

78 As per the Van Gend en Loos case and the classic affirmation that ‘the Community constitutes a new legal order of international law’: Case C-25/62, Van Gend en Loos v. The Netherlands [1963] ECR 1, 12.

79 Case C-162/96, Racke GmbH & Co v. Haptzollant Mainz [1998] ECR I-3655, para. 46. Also Case C-286/90, Anklagemyndigheden v. Poulsen and Diva Navigation [1992] ECR I-6019, para 9. Whether in Racke the Court accurately applied the rule allowing for treaty termination/withdrawal on the ground of a fundamental change of circumstances is doubtful; as noted in a leading textbook, the Court’s ‘relaxed interpretation’ was at odds with the position adopted by the ICJ in its case law: Crawford, supra note 55, 393–4.

80 Conclusions of the Work of the Study Group, supra note 2, at 178, para. 4.

81 F. Seyersted, Common Law of International Organizations (2008), at 396.

82 E.g., ibid., at 32–3.

83 See his account of constitutional limitations in Seyersted, F., ‘International Personality of Intergovernmental Organizations: Do Their Capacities Really Depend upon Their Constitutions?’, (1964) 4 Indian Journal of International Law 1 Google Scholar, at 23–5.

84 It should be noted that this may not have been Seyersted’s intention, given his insistence on the distinction between ‘the inherent external legal capacity to act on a voluntary basis as an equal partner and inherent internal jurisdiction over organs and their members as such – on the one hand – and extended power to exercise functional jurisdiction over or in … member states or private individuals … on the other hand’: supra note 81, at 69. Yet, perhaps because his main concern was to demolish the idea that the source of the rights, obligations and capacities of IOs is their internal law alone, he failed to give a more nuanced treatment to the constitutional question.

85 It was in this spirit that cases such as Reparation for Injuries (supra note 5) and Certain Expenses of the United Nations (Advisory Opinion of 20 July 1962, [1962] ICJ Rep. 151) were decided.

86 Cases that capture this idea include: Conditions of Admission of a State to Membership in the United Nations, Advisory Opinion of 28 May 1948, [1948] ICJ Rep. 57, at 64; Constitution of the Maritime Safety Committee of the Inter-Governmental Maritime Consultative Organization, Advisory Opinion of 8 June 1960, [ICJ] Rep. 150, at 170-1; and Legality of the Use of Nuclear Weapons in Armed Conflict, supra note 41, paras. 21–4.

87 Reparation for Injuries, supra note 5, at 178–80. The Court did not distinguish between the international and the institutional planes, but its conception of what the organization was under international law clearly informed its conclusion as to what the organization was authorized to do under the Charter.

88 Cf. Arts. 21 and 51 as adopted on first reading: YILC 2009/II, Part Two, at 47 and 67.

89 Commentary to Art. 22, YILC 2011/II, Part Two, at 72, para. 6; commentary to Art. 52, ibid., at 94, para. 8.

90 Joined Cases C-90/63 and 91/63, Commission v. Luxembourg and Belgium [1964] ECR 625, at 631 (concluding that ‘except where otherwise expressly provided, the basic concept of the Treaty [on the functioning of the EU] requires that the Member States shall not take the law into their own hands, except where otherwise expressly provided, the basis concept of the Treaty’).

91 Indeed, Special Rapporteur Gaja was hesitant to state a general rule on the issue: Gaja (Eighth Report), YILC 2011/I, Part One, at 99, para. 67.

92 A. Tzanakopoulos, Disobeying the Security Council: Countermeasures Against Wrongful Sanctions (2011), 154–90.

93 Ibid., at 157. This line of reasoning was compatible with the text of Arts. 22 and 52 as adopted on first reading.

94 Nolte, YILC 2009/I, at 11, para. 51.

95 See the discussion in T. Konstadinides, ‘Customary International Law as a Source of EU Law: A Two-Way Fertilization Route?’, (2016) YEL 513, at 519–25 (concluding that despite creating a ‘window of opportunity’ for claims based on custom to be made ‘the CJEU does not appear confident in exposing the EU to uncontrolled liability’ and ‘has demonstrated a blanket intolerance towards claims based on international custom’).

96 C-366/10 Air Transport Association of America and Others v. Secretary of State for Energy and Climate Change [2011] ECR I-13755, para. 107.

97 Ibid., para. 110. Previously, see Racke, supra note 79, para. 52.

98 Opinion of Advocate-General Poiares Maduro in Joined Cases C-402/05 P and C-415/05 P, Kadi and Al Barakaat International Foundation v. Council and Commission [2008] ECR I-635, para. 21.

99 Ibid., para. 21.

100 Ibid., para. 24.

101 Kadi, supra note 98, paras. 281 and 316.

102 Though Eeckhout offers a more nuanced reading of Kadi (‘The Integration of Public International Law in EU Law: Analytical and Normative Questions’, in P. Eeckhout and M. López-Escudero (eds.), The European Union’s External Actions in Times of Crisis (2016), 189, at 196–8), which puts the Court of Justice’s approach into context, his analysis also point to tendencies of the European judicial system to insulate itself from regimes of international law such as the World Trade Organization and the European System of Human Rights (at 200–203).

103 A. Gianelli, ‘Customary International Law in the European Union’, in E. Canizzaro et al. (eds.), International Law as Law of the European Union (2012), 93, at 100–1.

104 Ibid.

105 For a discussion of the ‘two masters’ dilemma with respect to the relations between international law and domestic law, see Crawford, J., ‘Chance, Order, Change: The Course of International Law’, (2013) 365 RCADI 13 Google Scholar, at 160–82.

106 This omission was reportedly deliberate: J. R Leiæ and A. Paulus, ‘Article 103’, in B. Simma et al. (eds.), The Charter of the United Nations: A Commentary, Vol. II (2012), 2010, at 2132–3.

107 E.g., Higgins et al., Oppenheim’s International Law: United Nations (2017), 427.

108 As discussed in Crawford, supra note 105, at 296–321.

109 Art. 24 UN Charter.

110 Leiæ and Paulus, supra note 106, at 2133.

111 Ibid., at 2127.

112 Al-Jedda v. United Kingdom, Judgment of 7 July 2011, 2011-IV ECHR, para. 105: ‘[i]n the absence of clear provision to the contrary, the presumption must be that the Security Council intended States within the Multi-National Force to contribute towards the maintenance of security in Iraq while complying with their obligations under international human rights law’.

113 In Accordance with International Law of the Unilateral Declaration of Independence in Respect of Kosovo, supra note 2, para. 118, the ICJ implies that Security Council resolutions can bind even non-state actors. But crucially, international organizations are not party to the UN Charter, and the basis on which they can be bound by UN law is unclear. See the discussion in commentary to Art. 67, YILC 2011/II, Part Two, at 104–5.

114 Art. 59 ARS; Art. 67 ARIO.

115 Commentary to Art. 67, YILC 2011/II, Part Two, at 105, para. 3.

116 I owe this example to a helpful exchange with one of the reviewers for this piece, to whom I am very grateful.