Many insurgents groups benefit from sanctuaries in neighboring countries where they are relatively safe from state security forces. These transnational insurgencies complicate traditional counterinsurgency operations in significant ways. Most importantly, transnational insurgencies have the potential to spark conflicts between neighboring countries. This monograph examines several transnational insurgencies that have been active since the end of the Cold War. While many neighboring countries have experienced the escalation of conflict between them as the result of cross-border violence, other states have successfully cooperated in providing border security. In depth case studies of relations between Rwanda and the Democratic Republic of Congo as well as India and its eastern neighbors are explored. The lessons learned from this research are applied to contemporary issues facing Iraq and Afghanistan.