Pro-government militias are a prominent feature of civil wars. Governments in Ukraine, Russia, Syria, and Sudan recruit irregular forces in their armed struggle against insurgents. The United States collaborated with Awakening groups to counter the insurgency in Iraq, just as colonizers used local armed groups to fight rebellions in their colonies. A now quite wide and established cross-disciplinary literature on pro-government nonstate armed groups has generated a variety of research questions for scholars interested in conflict, political violence, and political stability: Does the presence of such groups indicate a new type of conflict? What are the dynamics that drive governments to align with informal armed groups and that make armed groups choose to side with the government? Given the risks entailed in surrendering a monopoly of violence, is there a turning point in a conflict when governments enlist these groups? How successful are these groups? Why do governments use these nonstate armed actors to shape foreign conflicts, whether as insurgents or counterinsurgents abroad? Are these nonstate armed actors always useful to governments or perhaps even an indicator of state failure? How do pro-government militias affect the safety and security of civilians? The enduring pattern of collaboration between governments and pro-government armed groups challenges conventional theory and the idea of an evolutionary process of the modern state consolidating the means of violence. Research on these groups and their consequences began with case studies, and these continue to yield valuable insights. More recently, survey work and cross-national quantitative research have contributed to our knowledge. This mix of methods is opening new lines of inquiry for research on insurgencies and the delivery of the core public good of effective security.