The record of counterterrorism cooperation in the twentieth century illustrates well the barriers to its global governance. This chapter describes the evolution of global governance on counterterrorism in the pre- and post-9/11 periods, demonstrating the proliferation of cooperation over time. While the growth of cooperation in this field has often been contested, challenges to global governance have tended to yield more, not less, multilateralism. The chapter reflects on the causes and consequences of these developments. Changing patterns of cooperation are derivative of the changing threat environment. But global governance and counterterrorism occur within a political context, and states use international organizations (IOs) to advance and protect their interests, and influence others. Cooperation includes prominent roles for IOs, as well as regimes, trans-governmental networks, epistemic communities, and other institutional forms. The chapter concludes that the achievements and challenges of multilateral counterterrorism today contribute much to our knowledge of IOs and global governance.