This thesis examines Jemaah Islamiyah (JI), Southeast Asia's most dangerous terrorist threat. Since the group manifested its presence with its suicide bombings in Bali, Indonesia on October 12, 2002, considerable efforts have been devoted to describing the group responsible for the most damaging terrorist attacks in Southeast Asia and interpreting how it has changed over time. Over the course of the last decade, two competing interpretations of JI emerged. One view held that JI was divided between a large group of traditionalists and a smaller group of pro-violence militants. This became the conventional wisdom and served as the foundation for most countries' counterterrorism policies. The other held that the two factions worked closely together. By reconsidering JI's evolution in light of recently available evidence, this thesis shows that the second view more accurately describes JI. In particular, this thesis suggests that the two factions should be viewed as mutually supportive "administrative" and "operational" components of a single, adaptable terrorist group. To be successful over the long term, counterterrorism policies will need to pay greater attention to the administrative faction and its relationship to the operational wing, which conducts actual terrorist attacks.http://archive.org/details/jemaahislamiyahr109455060US Navy (USN) authorApproved for public release; distribution is unlimited.