To help policymakers understand and discuss the approaches to countering Islamic radicalization in the United States, the Center for Technology and National Security Policy conducted a study to assess both the nature of the threat and possible mitigation strategies. In Defense & Technology Paper No. 77, Samuel Musa and Samuel Bendett address the growing and evolving threat of domestic terrorism that is advocated and perpetrated by radical Islamic ideologues, as well as the emergence of the Internet as the battleground of ideas with the radical version of Islam. Over the past several years, the U.S.government and law enforcement agencies have become increasingly concerned with the spread and influence of Islamic radicalization amongst U.S. citizens and naturalized American individuals. Many such individuals are taking action intended to harm Americans and American interests domestically or abroad. Evidence points to a sophisticated and evolving indoctrination campaign that targets not just Americans of Muslim faith, but the larger population. It is becoming essential to view the spread of this radicalization as a technologically advanced phenomenon that should be addressed within the context of the evolving nature of the threat.