This book explores conditions under which non-state armed groups (NSAGs) participate in post-war security and political governance. It offers a comprehensive approach to post-war security transition processes based on five years of participatory research with local experts and representatives of former non-state armed groups. It analyzes successes and limits of peace negotiations, demobilization, arms management, political or security sector integration, socio-economic reintegration and state reform from the direct point of view of conflict stakeholders who have been central participants in ongoing and past peacebuilding processes. Challenging common perceptions of ex-combatants as "spoilers" or "passive recipients of aid", the contributors examine post-war transitions of these individuals from state challengers to peacebuilding agents. The book concludes on a cross-country comparative analysis of main research findings and ways in which they may facilitate a participatory, inclusive and gender-sensitive peacebuilding strategy.