In spite of the International Law Commission’s reluctance to recognize the direct incidence of non-State actors in the formation of customary international law, this chapter suggests that non-State actors can possibly matter in the formation of customary international law. After considering international law as an argumentative practice socially constructed, it will be claimed that customary international law is the product of successful argumentative campaigns carried out by international lawyers who usually work for States as well as those who represent the interests of other actors distinct from States. It will be posited that, although State lawyers’ views tend to be prioritized when identifying customary international law, considerations of lawyers working for non-State actors could be also take into account. It will be argued that the two-element approach to customary international law defended by the International Law Commission is just one possible perspective among many others. In this chapter, a social perspective of customary international law will be advocated with a view to defending that the community of international lawyers can possibly give weight to non-State actors’ positions in the formation of customary international law.

Against the backdrop of the inconclusiveness of Conclusion 4(2) regarding the role of international organisations in the formation of custom, this chapter elaborates on the reasons behind this lack of consensus and how this has affected the end-product of the International Law Commission’s work; that is the Conclusions incorporated in the International Law Commission’s 2018 Report. Such an enquiry is, according to this chapter, the key to addressing the shortcomings of the International Law Commission’s approach and to understanding whether the relevant Conclusion bears a strong normative claim to hardening into lex lata.

In 1995, the 26th International Conference of the Red Cross and Red Crescent mandated the International Committee of the Red Cross to prepare a ‘report on customary rules of international humanitarian law applicable in international and non-international armed conflicts’. The Study on customary international humanitarian law, published in 2005, identified 161 rules of customary international humanitarian law and presented the material collected in their determination. Complemented by regular updates of its practice part, the Study has also been accessible online via the International Committee of the Red Cross’s customary international humanitarian law database since 2010. For the Study, the International Committee of the Red Cross needed to consider many of the methodological questions that the International Law Commission faced in its work on the identification of customary international law. Like the International Law Commission’s Conclusions on that topic adopted on second reading in 2018, the Study is based on the fundamental requirement of two elements: a general practice that is accepted as law (opinio juris). Among the issues arising from this approach, there were the questions whose practice it is that forms rules of customary international law and whether actors other than States could be relevant in this context.

As the International Law Commission’s Conclusion 13 on the identification of customary international law provides, decisions of international tribunals can be considered a subsidiary means for the ascertainment of rules of customary international law. As this chapter argues, the real contributors appear to be the claimants who raise and shape the discussions about customary international law before a tribunal, which decides only on the basis of the pleadings and observations submitted by the parties. In that sense, investors have emerged as the most powerful claimants who certainly influence the clarification of rules of customary international law through investor–State dispute settlement.This chapter thus argues that investors exercise a significant influence over the tribunals’ rulings; and addresses the contribution of investors through the combination of two concepts – namely, ‘framing’ and ‘spilling-over effect’. The chapter unpacks both arguments through the study of the exceptions to the local remedies rule by examining the lex lata customary international law of diplomatic protection and emerging interpretations in investor–State dispute settlement, with a special focus on the ‘futility exception’ to the exhaustion of local remedies.

The chapter presents and critically assesses the view on non-State actors expressed in the Conclusions on Identification of Customary International Law adopted by the United Nations International Law Commission in 2018. Conclusion 4(3), setting the requirement of practice, stipulates that ‘conduct of other actors is not practice that contributes to the formation, or expression, of rules of customary international law, but may be relevant when assessing the practice referred to in paragraphs 1 and 2’ (i.e. practice of States and international organizations). Conclusion 9, dealing with the requirement of opinio juris, does not mention non-State actors at all. The chapter first traces the history of the conclusions in the International Law Commission work and then casts some doubt on the position that the International Law Commission has adopted in light of the views of other actors. It shows that the International Law Commission fails to do justice to the complex relationship that nowadays exists between non-State actors and customary international law.

decommissioning; Royal Ulster Constabulary; DavidTrimble; Holy Cross School; Ian Paisley; John Hume;Tony Blair

The chapter offers a constructivist account of the burgeoning roles non-governmental organisations have assumed in the making of customary international law. While most of these roles are informal, and their influence on the content and interpretation of customary international law norms has been primarily indirect, non-governmental organisations do contribute to the formation of customary international law through an increasingly diverse set of activities. Non-governmental organisation documentation, litigation, lobbying, and other forms of advocacy have contributed to treaty-making and ratification; to the domestication and internalisation of international norms and processes, including domestic accountability and remedies; and to codifying the obligations of, and stimulating practice by non-State actors such as business and armed groups. Despite a broad acknowledgement of the increasing involvement of non-governmental organisations in global governance by scholars and practitioners, their role in customary international lawmaking remains under-appreciated. To understand the increased influence of non-governmental organisations on the identification, formation, and application of customary international law rules, the chapter offers a differentiated, effects-based account of non-governmental organisation participation in customary international lawmaking.

peace process; republicanism; loyalism; UlsterUnionism; defeat thesis; stalemate;pan-nationalism