Civil resistance campaigns have led to some of the most important international developments in recent years, yet little is known of the role that civilian actors can play in challenging the use of violence by militant groups. This book examines the role that social mobilization in the Spanish region of Basque Country played in the decline and end of the Basque armed separatist group Euskadi Ta Askatasuna (ETA). For more than four decades, ETA waged a bloody campaign against the military and the Spanish and Basque police forces while causing a large number of civilian deaths. The Basque case demonstrates that civil resistance can work against terrorism, and this book will show that social mobilization is one of the factors that contributed to the failure of ETA's violent campaign. It reflects on how activism by the peace movement helped to delegitimise the armed struggle in society, explores the role civil society actors played in the construction of ideas that challenged ETA's political project, and highlights how civil resistance to the armed group undermined the prestige of militants and helped to limit the social reach of violent extremist narratives. Resisting Terror raises awareness of the importance of collective action, not only against regimes but also non-state militants, and highlights the significance of civil activism as a tool to mitigate political violence.