Why should we care about how domestic courts must interpret international law? In this chapter, I provide an overview of the existing literature dealing with the interpretation of international law by domestic courts, both in Switzerland and in other jurisdictions (2). I explain the reasons that lead me to focus on Switzerland (3), courts (4), domestic courts (5), and international law (6). Finally, I clarify why it is worthwhile to examine the domestic practice from the angle of interpretative methods (7).

In 2014, the Swiss Federal Tribunal mentioned international law in 27.3% of its published decisions. By contrast, six decades...

Before digging into the details of the domestic judicial practice of international law, some conceptual and terminological clarifications are in order. First of all, what do lawyers – as opposed to musicians, dancers, or physicists, for example – do when they interpret? What do they mean by interpretation (2)? Second, what is judicial interpretation (3) and what is domestic judicial interpretation (4)? Third, I clarify the notion of interpretative method (5). Finally, given that the present study is concerned with the interpretation of international law, it is important to delineate what this body of law encompasses (6).

Interpretation can be...

In this chapter, I highlight several characteristics of the Swiss legal order that deserve emphasis for the purposes of this study.²⁷⁷ These characteristics fall into three categories. A first cluster of features pertains to the relationship between the Swiss State and international law (2). It encompasses the characteristics, principles, and goals of Swiss foreign relations law and policy (2.1), and the way the Swiss legal order regulates its relationship with international law (2.2). I then highlight a series of principles of political organization that govern the Swiss State (3): federalism (3.1), linguistic diversity (3.2), the rule of law (3.3), semi-direct...

In this chapter, I examine the legal effect of domestic rulings in international law. I argue that this effect is both static and dynamic.⁸¹⁷ First, domestic courts enable States to respect their international obligations. They do so by enforcing international law domestically (infra, section 2). Second, from the perspective of the sources of international law, domestic judicial decisions also have a dynamic effect on international law, as they contribute to shaping it, on the one hand, and help interpreters ascertain it, on the other hand (infra, section 3).⁸¹⁸ I explain my reasons for focusing on art. 38 ICJ Statute in...

In Parts 1 and 2, I have analyzed what interpretation is, and why domestic courts’ interpretations are central to international law. I now move on to a third question: how must domestic courts interpret international law?

In the third part of this book, I argue that international law requires States to use specific methods to interpret these obligations, including via their courts, and that there are good reasons for imposing such a requirement on them. These reasons are primarily connected to the importance of lawful interpretation. However, they can also be linked to the virtues of predictable, clear, and consistent...

In Chapter 5 (supra), I have stressed that interpretative methods guide domestic and international legal practice, and that there are good reasons for requiring judges to abide by them. I have not yet examined the specific interpretative methods of international law, and the reasons for using these methods in particular.

The present chapter is devoted to these issues. These questions matter because States (including courts) must know what methods the law requires them to apply, and because the addressees of legal decisions must know by which standards States and their authorities should be held accountable. Moreover, it is essential to...

The law of treaties represents the great bulk of the domestic judicial practice of international law. This also applies to the Swiss practice, as empirical find­ings show.¹³⁷²

Treaties ratified by Switzerland span a wide number of substantive areas,¹³⁷³ including IHRL, migration, diplomatic relations, copyright, civil aviation, and investment protection, and including both public and private international law.¹³⁷⁴ Treaties can be bilateral or multilateral. They can provide short-term answers to specific issues, or establish long-term cooperative schemes. They can generate interstate or intrastate rights and duties.

‘[T] reaties’, Philip Muntz reportedly said in the House of Commons in 1871, ‘like piecrusts,...

While treaty law is undoubtedly the source of international law that is most frequently used in domestic courts, it is not the only one. Besides written international legal acts, courts also apply unwritten ones, namely customary international law (CIL) and general principles of international law.¹⁷¹⁹

Compared to treaty law (supra, Chapter 7), there is little domestic judicial practice pertaining to CIL, and this practice is often more ‘hesitan[t] ’.¹⁷²⁰ This a fortiori applies to general principles of international law, which are barely cited. As I will explain, courts’ fluctuating terminology¹⁷²¹ makes it hard to identify the few cases dealing with...