International law has conducted and still conducts distinctive societal functions based on the general understandings and perceptions of law. In this article, I first quickly glance at two disciplines, international law and international relations, and see how they have developed as separate disciplines, scarcely learning from each other until recently. In the second section, I deal with the longstanding debates on the binding force of and compliance with international law from a functional perspective. In the third section, I seek to demonstrate that although bindingness is the primary function of international law, the raison d'etre of international law must be explained by means of more comprehensive perspectives. In the final section, I indicate functions other than the binding one, and seek to elucidate how they carry out important societal functions which non-legal norms, such as ethics, morality and religion, as well as policies or politics, cannot fulfil. In this way, I seek to explore the raison d'etre of international law in terms of its societal functions, in comparison with those of international politics (or policies) and international ethics (or morality), by analysing four functions of international law: binding, communicative, value-declaratory, and justifying and legitimating.