This book argues that it does not suffice to simply invoke and demonstrate the two constitutive elements of customary international law, practice and opinion juris, to successfully and plausibly make a claim under the doctrine of customary international law. Behind what may look like a very crude dualist type of legal reasoning, a fine variety of discursive constructions are at work. By unpacking these discursive constructions, the book depicts the discursive splendour of customary international law. It reviews eight discursive performances at work in the discourse on customary international law and makes a number of original and provocative claims about this aspect of law. For example, the book claims that customary international law is not the surviving trace of an ancient law-making mechanism that used to be found in traditional societies. Indeed, as is shown throughout, the splendour of customary international law is everything but ancient. In fact, there is hardly any doctrine of international law that contains so many of the features of modern thinking. The book also puts forward the idea that all discursive performances of customary international law are shaped by texts, are articulated around texts, echo and continue pre-existing texts, unfold in a textual space, or, more simply, originate in a text-constituted environment.