The range of methods that courts can use for the interpretation of customary law is in principle no different than that applicable to other sources of international law, and these methods roughly correspond to those enumerated in articles 31-33 VCLT. At the same time, not all these methods are suitable for the interpretation of customary rules of international environmental law (IEL). Most environmental rules have by their inception an inherent constraint with regards to teleological interpretation as they yield to a number of considerations beyond simply the protection of the environment. In light of this, international courts and tribunals have interpreted customary environmental rules in expansive as well as regressive ways, oscillating between these two tendencies. When interpreting expansively, courts take into account developments that appear to affect the rule in question and push it to catch up with these developments. In contrast, regressive interpretation involves а backward looking approach where the courts are content with offering an interpretation that diverges from the standards surrounding the rule and renders a more conservative version of it.

This Conclusion sums up the main arguments in the book, addresses some final questions, and suggests some future directions of travel. In particular, it returns to the eugenics question, and examines whether current practices in modern liberal states might be in line with a type of eugenics that does not involve state coercion, but that rather involves manipulation, and chiefly the manipulation of women. It also emphasises how an analysis of individual choice should be a secondary concern in our approach to the ethics of selecting against disability, and that the position of the state should be our starting point. The last part of the chapter offers additional reflections on the topic of starting points, and on the importance of thinking further about the nature of pregnancy.

This chapter examines the interpretation practice of international investment tribunals, using the territoriality requirement in international investment arbitration as a case study. International investment tribunals employ various interpretative methods when interpreting the scopes ratione loci and ratione materiae of investment treaties. However, on many occasions arbitral tribunals use methods of interpretation that favor the object and purpose of treaties over other elements of interpretation envisaged in Articles 31–33 of the VCLT. When applied to the interpretation of the territoriality requirement, arbitral tribunals interpret the requirement based on the intention of the contracting parties to create favourable conditions for the promotion of investments and economic cooperation. Such an interpretive approach creates an expansive tendency of the territorial application of investment treaties.

This chapter addresses a number of foundational issues in relation to the position of the modern liberal state and the use of techniques and procedures that can prevent the birth of a disabled child. It begins by explaining why the traditional approach to the ethics of selective reproduction is insufficient as it usually sidelines or minimises the role of the state, following on from a common assumption that the state is neutral. It then considers the meaning of a liberal commitment to neutrality, so that we can analyse and question this common assumption. Among other things, the chapter claims that the relevance of the role of the state is not limited to the use of coercive measures, and that we should focus on state intention. Although neutrality can be a matter of degree, and while there are different interpretations of a neutral state intention, the chapter suggests that the position of the state can be assessed by reference to certain central liberal commitments. In particular, the chapter examines the importance of individual choice as an essential commitment of the modern liberal state, and considers what choice should be available to prospective parents.

The chapter analyzes the ’principle of single undertaking’ of the World Trade Organization (WTO) Dispute Settlement System (DSS). The principle of single undertaking is a unique feature of the WTO, and refers to the fact that the WTO treaty comprises several agreements all of which bind WTO members simultaneously and cumulatively, thus requiring implementation as a single undertaking. In order to maintain coherence within this single undertaking, the WTO DSS has engaged in horizontal cross-fertilization of jurisprudence across agreements. This is done by reliance on the tools and methods of treaty interpretation as defined by the VCLT rules of interpretation and their customary counterparts.

This chapter examines the collective interpretative practices of non-judicial actors, with a special focus on the One Ocean Hub. The One Ocean Hub is an inter- and transdisciplinary ocean research network that engages academic and non-academic stakeholders, including local decision-makers and representatives from international organizations, civil society, and affected communities, to co-develop mutually supportive interpretations of international environmental law, the law of the sea, and international human rights law. The interpretative practice of the One Ocean Hub related to the protection of human rights that are dependent on a healthy ocean is an example of collective interpretation whose authority comes from the expertise of the involved practitioners. The chapter examines how this expertise-based interpretation can be institutionalized under the law of treaties, with a view to embedding it in the work of relevant treaty bodies.

This chapter provides a detailed genealogy of the development crimes against humanity, from its nineteenth century natural law origins through its codification in the Rome Statute, and finally its possible recodification in a new treaty. It subsequently traces the interpretative approaches of states towards the current draft proposal about a specialized treaty, ultimately concluding that states’ attitudes may fall into one of three categories – unity, evolution, or diversity. Unity refers to states who advocate for the new treaty to be a horizontal add on to the Rome Statute, making the two instruments consistent as a matter of text and application. Evolution, refers to states who advocate for the progressive interpretation of existing provisions, with a view to adjusting the definition of crimes against humanity consistently with new development, or expanding the list of crimes that fall in this category. Diversity, finally, refers to the possibility of states to continue developing the law even after codification, through evolutions in customary law or diversity in national codification.

International law formation through treaties and customary international law is inherently based on a private law paradigm characterized by bilateralism and consensualism. For the most part, this private law paradigm permeates into the process of interpretation as reflected in Articles 31–33 VCLT. That said, the principle of ‘systemic integration’ enshrined primarily in Article 31(3)(c) VCLT and its customary counterpart presumes a systemic structure of international law. In this context, obligations erga omnes, jus cogens norms, and, to some extent, general principles of law provide for at least a rudimentary public law framework, which dilutes consensualism and enables a certain degree of systematization of treaty and customary law. Such systematization then takes places through the process of interpretation and, more specifically, systemic integration. Underlying this analysis is the claim that the rule of interpretation requires the systemic integration of the rules of international law ‘regardless of the source from which these rules may be stemming’

Processes of national implementation of the Rome Statute of the International Criminal Court (ICC) represent a relevant interpretive practice when it comes to this treaty. When adopting implementation legislation, states effectively offer their interpretation of the Rome Statute, sometimes diverging from the way that the ICC interprets this treaty. The chapter focuses of such examples of divergent interpretations, in order to establish whether divergent interpretations by states might influence the way the ICC interprets the Rome Statute. As an international treaty, the interpretation of the Rome Statute is governed by the rules of interpretation as enshrined in the VCLT. In light of this, divergent interpretations by states might need to be taken in consideration by the ICC in its interpretation, for example as subsequent agreement within the meaning of Article 31(3)(b) of the VCLT. Ultimately, while it remains necessary to distinguish between an interpretation within the scope of the existing law and modification of the text of a treaty, judges of the ICC may rely on the VCLT rule of interpretation in order to account for the interpretative practice of states.

Interpretation is part and parcel of every juridical endeavour. In international law, the law and methods pertaining to the process of interpretation continue to vex international legal theory and practice; in fact, increasingly so. The provisions of the Vienna Convention on the Law of Treaties (VCLT) on treaty interpretation reflect three premises which can have broader implications for the practice of interpretation in international law. First, they reinforce the idea that interpretation is, or at least can be, a formal process based on legal rules.Second, this process determines the content of rules that are ‘in force’ and is thus legally and analytically distinct from the processes of identification, modification, amendment, and termination of rules. Third, these legal rules can have a general scope of application in the sense that they can apply regardless of the nature or subject-matter of the rule to be interpreted and irrespective of who performs the interpretation. That is to say, the VCLT envisages the possibility of a law of interpretation that forms essentially ‘a unity’

There are four different scenarios when the institutional context of an organization is relevant in the interpretation of customary international law. Based on these scenarios, the following observations about interpretation in the institutional context can be made. Firstly, the separate institutional sphere of an organization adds a layer of normativity and authority next to that of general international law. Therefore, it may happen that instruments created by the organization would have normative effect within the institutional framework, but not per se in general international law. Conversely, a rule of customary international law could be of uncontested validity but not have normative force automatically within the institutional framework. Secondly, within the institutional framework, conduct of the organization may not be readily distinguishable from the conduct of member states. This may then influence the identification of potentially new customary rules. Finally, it seems that the institutional context is conducive to the teleological method of interpretation.