The emphasis of counter-terrorism policy in the United States since Al Qaeda's attacks of September 11, 2001 (9/11) has been on jihadist terrorism. However, in the last decade, domestic terrorists, people who commit crimes within the homeland and draw inspiration from U.S.-based extremist ideologies and movements, have killed American citizens and damaged property across the country. In this respect, domestic terrorists are a widely divergent lot, drawing from a broad array of philosophies and world-views. These individuals can be motivated to commit crimes in the name of ideas such as animal rights, white supremacy, and opposition to abortion. The expression of these world-views, as opposed to violence in support of them, involves constitutionally protected activities. This book provides background regarding domestic terrorists, detailing what constitutes the domestic terrorism threat as suggested by publicly available U.S. government sources and potential issues for Congress.