Multilateral Principles in a Bilateral World

Multilateralism in international investment law is a multifaceted concept with a complex and eventful history. Multilateralism is a paradigm for international investment relations and is also present in the caselaw of investment arbitral tribunals, regardless of whether they consider bilateral or multilateral investment treaties. Indeed, in most cases, they interpret treaty provisions as part of a multilateral system. Further, multilateralism is present every time States act in concert with other States or consider other States’ investors’ legitimate interests. It also emerges that, in some instances, multilateralism has become mandatory. For example, this is the case concerning sustainable development or climate change. In these areas, international law requires multilateralism. States are under an obligation to co-operate for purposes of achieving or promoting multilateral solutions. However, concerning the international investment law context, such a concept is not present. The general assumption is that States’ participation in multilateral practises is left to their discretion: it is voluntary or consensual. In this article, we question that assumption. In this article, we offer a brief review of multilateral experiences in international investment law in the 20th century and provide an analysis of multilateralism in a historical context. Then we turn our attention to the current state of affairs to appreciate it in light of the past. Further, we discuss the future, and in particular, mandatory multilateralism in international law with respect to sustainable development. Here we identify the principles, which might justify mandatory multilateral approaches. Finally, we consider whether the principles justifying mandatory multilateralism in international law are applicable in the context of international investment law as well. We attempt to answer this question in the affirmative and point out further areas of research.