Following its overthrow of Saddam Hussein in 2003, the United States was confronted with one of the most complex state-building enterprises of recent history. A central component of state building, emphasised in the literature yet given scant attention at the time of the invasion, is the process of political reintegration: the transformation of armed groups into political actors willing to participate peacefully in the political future of the country. In Iraq, political reintegration was a particularly important challenge, relating both to the armed forces of the disposed regime and to the Kurdish and Shia militias eager to play a role in the new political system. This article examines the different approaches employed by the United States toward the political reintegration of irregular armed groups, from the policy vacuum of 2003 to the informal reintegration seen during the course of the so-called “surge” in 2007 and 2008. The case study has significant implications for the importance of getting political reintegration right—and the long-term costs of getting it badly wrong.