Introduction

Since the 1990s, the use of constitutional language has gained increasing popularity in international legal parlance. This increased popularity has made it difficult to come up with a single and coherent definition of ‘international constitutionalism’. The vocabulary of constitutionalism has been used in different contexts and for different purposes, varying from in-depth critiques of existing international law to attempts to explain the rise of international tribunals, the revitalisation of international organisations, the self-understanding of European organisations in terms of constitutionalism or the development of a core of fundamental values in international law. Moreover, well before the 1990s, international lawyers already used the term ‘constitution’ to refer to the founding treaties of international organisations.

In this chapter, I will not deal with all these different ways in which the language of constitutionalism is used. Rather, I will focus on one – albeit still broad – way in which it is employed in international law: as an attempt to explain existing developments in international law in terms borrowed from domestic constitutionalism, with the aim of furthering a normative agenda of internationalism, integration and legal control of politics. This way of using the language of constitutionalism is based on two desiderata: to remain within the boundaries of positive law, and to contribute to a normative, internationalist project.