International institutions provide a structure for cooperation among states, but they also insert themselves into national and local political spaces, as conveyors and propagators of international norms in domestic spaces, “third-side” providers of good offices brokering between governments and society, and providers of resources to help address problems. The UN and the ICC played a direct role in influencing the process and outcomes of political responses to the conflict in Colombia. The UNHCR and UNDP shaped the treatment of victims, targeting of funding, and the political incentives for peace. The ICC pushed negotiators to incorporate international transitional justice norms embodied in the Rome Statute against impunity. This chapter traces the mechanisms through which these international institutions have penetrated domestic political spaces for peace in Colombia.