This chapter explains the cosmopolitan nature of the law of peacebuilding per se and, second, identifies laws and international developments that have indirect effects on peacebuilding and peace law by creating a process of building peace. The practices of states and other actors and their expectations of appropriate conduct create a dialectic that makes legal obligations a cost that states must calculate in their decisions to comply with hard and soft law requirements, obligations, and contested or denied responsibilities. We compare international lawas cosmopolitanism to the other major paradigms used to explain peacebuilding success and failures -- realism, liberalism, constructivism -- demonstrating the ways in which our approach complements and diverges from these approaches. We next discuss the concept of a human right to peace and then address peace as an outcome of international law. We conclude this chapter with some thoughts about the importance of the development of peace law.