The preceding chapters demonstrate that domestic law has been used by international courts and tribunals in a variety of different ways to interpret international legal rules or instruments. Each instance of comparative reasoning is inextricably linked to the legal and historical context in which it occurs and in which the court or tribunal operates. The novelty of the specific legal regime, the presumed knowledge of other states parties or the presence of nebulous treaty standards are all factors that have led to the use of domestic law as a means of interpretation. As such, drawing general conclusions from a study such as this is difficult.

The Dispute Settlement Mechanism (DSM) of the World Trade Organization (WTO) is the compulsory, binding inter-state adjudicatory system for disputes between member states related to WTO law. The panels and the Appellate Body (AB) that work under the framework of the DSM have gained a reputation for judicious and effective dispute resolution in the international sphere, leading them to be hailed as a guiding light for other international courts and tribunals. Although fact-intensive cases are the norm in the WTO DSM, the legal questions that come before panels and the AB are primarily questions of treaty interpretation and hence hold interest for any study of legal interpretation.3

Of the courts and tribunals surveyed in this book, those that deal with inter-state disputes have been most reticent to invoke domestic law to interpret international law. Some commentators have suggested that this may be due to a concern of bias towards the cited countries, a remark that certainly seems to have weight and perhaps explains why the courts and tribunals examined in this and the following chapter have tightly circumscribed their reference to domestic law, generally limiting the cited law to the parties to the case at hand.

However, other factors would also seem to distinguish inter-state courts and tribunals from those examined in subsequent chapters. The most obvious of these is the weaker analogy between domestic law and international law related to inter-state affairs, insofar as the latter aims to regulate the actions of states, not individuals. Whilst international criminal law, human rights law and international investment law arguably have clear parallels with domestic criminal law, constitutional law and public and administrative law, respectively, the rules regulating inter-state conduct have traditionally been analogised to domestic private law, especially to the law of contracts and trusts, and more recently to constitutional and public law. Yet, there are evident limits to how far these analogies are applicable to inter-state relations.

This chapter and the following chapter explore the use of domestic law by two inter-state courts and tribunals. This chapter examines the jurisprudence of the International Court of Justice (ICJ), whilst the following chapter analyses the case law of the panels and Appellate Body of the World Trade Organization (WTO). Although the cases examined vary significantly in terms of subject matter, certain common themes are identifiable. In particular, the relatively rare instances in which domestic law has been used raise questions regarding the circumstances in which domestic law may indicate the intention of a state.

In the late spring of 1992, the Secretary-General of the UN delivered a report to the Security Council that captured the attention of the international community. Yugoslavia – from which Croatia and Slovenia had declared independence less than a year before – had fallen into a pitched civil war fuelled by bitter ethnic tensions between Serb, Croat and Muslim communities. Nestled in the centre of the former unified state, the nascent republic of Bosnia-Herzegovina became the scene of atrocities not seen since the Second World War. The Serbs of Bosnia-Herzegovina, the Secretary-General reported, were making a ‘concerted effort … to create “ethnically pure” regions’ in the Republic,2 employing tactics that ‘were as brutal as they were effective’. Reports on the situation documented the grim scene: the killing or displacement of 2.1 million Bosnians by the summer of 1993, the systematic rape of women and girls and the operation of 715 detention centres in which rape, torture and execution was commonplace.

The interaction between domestic law and international law is a topic of perennial interest for international lawyers. Domestic law has long been recognised as a source of international law, an inspiration for legal developments or the benchmark against which a legal system is to be assessed. Often, it is simply treated as mere fact, indicative of the legality of a state’s actions. Academic commentary normally re-traces these well-trodden paths, leaving one with the impression that the interaction between domestic and international law has been thoroughly mapped, and is unworthy of further enquiry. However, a different – and surprisingly pervasive – nexus between the two spheres has been largely overlooked: the use of domestic law in the interpretation of international law. The present book aims to fill that gap in the literature.