The purpose of this study was to systematically examine the impact of non-governmental (NGO) and other civil society organizations on the creation, implementation, and durability of a peace agreement following a civil war. A most similar systems comparative study of three conflicts in Southeast Asia--Aceh, Indonesia; Mindanao, Philippines; and the Tamil separatist war in Sri Lanka--examined the level of impact of NGO and other civil society activities on the peace processes in those conflicts. NGOs and civil society organizations employ a variety of techniques to shape the peace process toward an enduring agreement. Civil society in a region that is representative of the broader public and unified in its aims for peace is most likely to have an impact on the peace process. Early and sustained engagement with the public and international community leverages NGO influence over peace negotiations. Partnerships between international NGOs and local organizations also increase the likelihood that a peace agreement will be implemented and remain in force.