Attention to extreme forms of political violence in the social sciences has been episodic, and studies of different forms of political violence have followed different approaches, with “breakdown” theories mostly used for the analysis of right-wing radicalism, social movement theories sometimes adapted to research on left-wing radical groups, and area study specialists focusing on ethnic and religious forms. Some of the studies on extreme forms of political violence that have emerged within the social movement tradition have nevertheless been able to trace processes of conflict escalation through the detailed examination of historical cases. This article assesses some of the knowledge acquired in previous research approaching issues of political violence from the social movement perspective, as well as the challenges coming from new waves of debate on terrorist and counterterrorist action and discourses. In doing this, the article reviews contributions coming from research looking at violence as escalation of action repertoires within protest cycles; political opportunity and the state in escalation processes; resource mobilization and violent organizations; narratives of violence; and militant constructions of external reality.