Jus cogens is a formidable yet elusive concept of international law. Since its incorporation in the Vienna Convention on the Law of Treaties some 35 years ago, it has made tentative inroads into international legal practice. But its role in international law is arguably less prominent than might have been expected on the basis of its powerful potential and in view of wider developments in international law that call for constitutionalisation and hierarchy, including the processes of fragmentation and humanization. This volume of the Netherlands Yearbook of International Law sets...