Soft law is often seen as a way to overcome certain problems of legitimacy in international law, notably the weaknesses of a voluntaristic conception of international law's validity. Other perceived benefits of soft law include flexibility, speed of adoption and modification, and even effectiveness. Yet, soft law is seen by others as a threat to law, because it effaces the border between law and politics. This paper explores different approaches to the boundary between law and not-law that seek both to maintain this boundary and to reconceptualize it in a way that better anchors the validity of international legal rules.