The traditional approach to international law granted states an absolute monopoly in making international law and it discussed the rights and powers of states as a sole subject of international law. However, the proliferation of norms made by non-state actors raises questions with regard to the status of the actors as well as the legitimacy of the norms in the international fora, while it also challenges the state-centric orientation of international law. In consideration of the foregoing, customary law—whichwas traditionally comprised of two statebased elements of practice and opinio juris, as an important source of international law—has been faced with a strand of inquiry: can non-state actors generate international customs? Through 1) an in-depth survey of scholarly arguments regarding law-making in certain circumstances that could also belong to private parties; and 2) a close examination of the lex mercatoria as an example of existing international customs developed by non-state actors, this article tries to clarify a) the legitimacy crisis of a more inclusive approach to international law and b) proposes opportunities whereby non-state actors could participate in the law-making process.
