Many armed groups create informal institutions to maintain social order during conflict. The remnants of these informal institutions form a key challenge for governments in postconflict societies in their attempts to reestablish themselves as credible state authorities. The persistence of paramilitary groups’ informal “justice” systems in the form of so-called punishment attacks in Northern Ireland, more than twenty years on from the Good Friday Agreement, offers insights into the legacy of wartime institutions. We argue that armed actors can benefit from the social control wartime institutions grant them long after the conflict ends and both armed actors and civilians are socialized into relying on these institutions. Building on research on wartime institutions, criminal governance, and postwar state-building, we examine how the informal “justice” systems created during the Troubles (1968–98) remain at the fringes of postwar society, drawing on historical works, interviews with stakeholders, geocoded data on “punishment attacks,” and survey data.