Politics and law appear deeply entwined in contemporary international relations. Yet existing perspectives struggle to understand the complex interplay between these aspects of international life. In this path-breaking volume, a group of leading international relations scholars and legal theorists advance a new constructivist perspective on the politics of international law. They reconceive politics as a field of human action that stands at the intersection of issues of identity, purpose, ethics, and strategy, and define law as an historically contingent institutional expression of such politics. They explain how liberal politics has conditioned modern international law and how law ‘feeds back’ to constitute international relations and world politics. This new perspective on the politics of international law is illustrated through detailed case-studies of the use of force, climate change, landmines, migrant rights, the International Criminal Court, the Kosovo bombing campaign, international financial institutions, and global governance.