International Tax Law and Customary International Law

Abstract

Abstract This chapter examines the relationship between international tax law and customary international law (CIL). CIL refers both to the process through which certain rules of international law are formed and the rules themselves formed through such a process. No consensus has been reached, however, regarding the concept. Nevertheless, when establishing the sources of international law, article 38 of the Statute of the International Court of Justice indicates the two constituent elements that manifest the existence of a customary rule. Moreover, the International Law Commission has shed light on how CIL rules are identified. Traditionally, the literature has focused little on custom in international tax matters, probably because international tax law (if it exists as such) is treaty-based. The use of double taxation conventions as a (bilateral) mechanism to prevent double taxation has resulted in a large network of tax treaties. But even if international tax law is eminently based on treaty rules, the question is whether these treaties contain rules that do in fact reflect CIL.