This chapter addresses the role of international organisations in the formation of customary international law from a specific viewpoint: whether international organisations, which knowingly have many instruments to shape the behaviour of States, are also capable of shaping the opinio juris of States. For instance, would an international organisation such as the United Nations be able to promote, or at least influence the formation of opinio juris that is consistent with findings and recommendations of the Intergovernmental Panel on Climate Change? To develop my argument, I organise the chapter in two main parts – a study into the concept of opinio juris, and a study into the ability of international organisations to promote opinio juris with a desired content. This work concludes by playing down the possibility that international organisations are able to coordinate international processes in a manner to shape opinio juris pursuant to desired standards.

This chapter argues that international organisations can be conducive to the emergence or consolidation of the customary status of those primary rules of international law which their sanctions are meant to vindicate. It shows that the contribution of sanctions to the formation of custom varies significantly depending on the concrete situation. In cases where international organisations react to breaches of obligations that already have an erga omnes status and their standing to adopt sanctions is uncontested under the law of countermeasures, international organisations contribute to consolidation and clarification of custom. Ironically, however, the potential for customary law-making is greater when the erga omnes status of an obligation towards which an international organisation is reacting to is not yet confirmed. The illegality or legal uncertainty shrouding such sanctions under the law of responsibility does not preclude their potential in customary law-making – in fact, it may maximise their contribution. In discussing these situations, the present chapter makes an important distinction between the act of sanction and the act of protest. This makes it possible to argue that it is protests accompanying the act of sanction that have a role to play in custom-making, rather than the act of sanction itself.

This chapter seeks to shed light on the role of non-State actors in custom-making processes. It does so by repudiating the dominant understanding of opinio juris and practice within the two-element variant of the doctrine of customary law that has informed practice and scholarship since the 1920s. It shows that dominant approaches to opinio juris and practice are indifferent to the role of non-State actors by virtue of constructions that are highly questionable. Section 1 sketches the dominant understanding of two elements of customary international law. Section 2 discusses the limitations of the dominant understanding of opinio juris by showing the extent to which the anthropomorphic concept of opinio juris fails to perform the functions assigned to it. In section 3, the attention turns to practice which contains a greater variety of approaches. This section particularly emphasizes the role of domestic non-state actors in the creation of international norms that shapes State practice, and increasing role of international organizations to strengthen the grips of the domestic actors in creating international customary norms through the member States. This chapter ends with a few concluding remarks about the general implications of the approach promoted here for the doctrine of customary law as a whole.

This chapter reflects on the last decade of scholarly reflections on the question of non-State actors and customary international law and revisits some of the specific argumentative constructions and presuppositions that have informed – and continue to inform – discourses on the contribution of non-State actors to the formationof customary international law. It is argued here that three tropes have been mechanically repeated in previous rounds of scholarly debates on non-State actors and customary law. These constructions can be summarised as follows: the idea that the two-element variant of the doctrine of customary international law originates in article 38 of the Statute of the Permanent Court of International Justice; the continuous attachment of international lawyers – including the International Law Commission – to the distinction between practice and opinio juris; the understanding of the concept of non-State actors as a plain and innocent descriptive category.

This chapter examines the role of resolutions in the International Law Commission Conclusions on Identification of Customary International Law. The analysis unfolds along three lines of inquiry. The first one critically analyses the methodology devised by the International Law Commission to ascertain the existence of a customary rule with a view to understanding how it works in the institutional setting of international organizations. The second one examines the definition of resolution contained in the Conclusions and compares it with the mainstream literature on the concept of resolution. The third one evaluates the practical implications of the International Law Commission Conclusions by using the resolutions of the United Nations General Assembly as a case study. An argument is made that the International Law Commission Conclusions do not add either certainty or sophistication to the process of ascertaining customary rules, thus failing to provide authoritative guidance to practitioners in the field of international organizations’ practice.

This chapter addresses the manner in which the International Law Commission sees its own output in relation to custom. While in the Conclusions and Commentary on the Identification of Customary International Law it dedicates specific sections to ‘teachings of publicists’ and judgments, the Commission chose not to dedicate a sub-heading to its own work, instead mentioning it in passing in the commentary preceding the ‘Significance of certain materials for the identification of customary international law’ section. This chapter argues that the Commission did not appropriately grapple with its own role in relation to custom: despite the peripheral participation of States in its work, the International Law Commission’s output has at times fundamentally shaped customary rules, and this is not reflected in the Conclusions and Commentary. The chapter concludes that the problematic position of the International Law Commission on this subject is the triumph of pragmatism over accuracy. This is symptomatic of deeper problems with the project as a whole – the artificiality of the two-element approach, the excessive emphasis on State practice, and the impossibility of extricating ‘identification’ from ‘formation’ of custom. A closer look at the Commission’s purported mirror-image reveals distortions more akin to a looking-glass.

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The International Law Commission held that that the conduct of non-State actors ‘is not practice that contributes to the formation, or expression, of rules of customary international law’ for the sake of the identification of customary international law. However, the present chapter argues that the activities of de facto regimes can be considered as properly speaking ‘practice’ that contributes to the formation, or expression, of rules of customary international law under two scenarios. Firstly, the custom-creating or custom-strengthening conduct of the de facto regimes might be attributed to a State, usually to an occupying power or a State supporting in various means the entity by exercising effective control or at least decisive influence over it. Secondly, de lege ferenda, even without attribution, the conduct of de facto regimes should be taken into account as strengthening the practice forming customary international law at least in subject matters governing the rights and obligations of the de facto regimes itself. This chapter argues that in both scenarios the de facto regimes’ law-making capacity and conduct should be taken into account either as relevant sources for identifying the ‘practice’ of States or the conduct of international organisations, or as relevant ‘practice’ as such.

The role of international organisations in the formation and expression of customary international law remains quite controversial as shown in the works of the International Law Commission leading to the adoption on second reading of the draft conclusions on identification of customary international law. As an international organisation of a universal character, the United Nations holds a unique place in this regard. The contribution of some of its organs to the formation and/or expression of rules of customary international law is complex and manifold. It may be direct, or indirect; and it bears a close link with the States’ reaction to positions taken by the relevant United Nations organs. This chapter examines the specific contribution of the United Nations Secretariat to the formation and expression of rules of customary international law. Such contribution is apprehended through various forms of conduct of the Secretariat, including legal opinions of the Secretariat, the Secretary-General’s practice relating to multilateral treaty depositary, and the interaction between the Secretariat and other United Nations organs. Based on this analysis, it is advanced that the United Nations Secretariat plays a direct and indirect role in the formation and expression of rules of customary international law.

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