This contribution aims to consider regionalism and the unity of international law from a practical, legal positivist perspective. The analysis will focus on the interrelationship in terms of validity, sources, and questions of (non-)application and conflict. A tentative conclusion is that regionalism as such does not form more of a threat to the unity of international law than other phenomena. All may equally lead to the misinterpretation, non-application or even violation of international law. One may recast the suggested tension between regionalism and the unity of international law into two much more generally problematic features of international law: the lack of hierarchy between and within the sources of international law or obligation; and the rudimentary relationship between a domestic or regional legal system and international law at large. What would or should remedy these two features endemic to the international legal order is, quite naturally, open to discussion.