Both domestic and international terrorist organizations employ guerrilla warfare tactics, techniques, and procedures. Thus, the ability to identify and defeat the members of these organizations, cripple their infrastructures, and disrupt their financial resources lies in the understanding of modern guerrilla warfare as it develops in the twenty-first century within the United States.3 The forms of asymmetric warfare4 adopted by domestic and international terrorist groups alike is no longer intended to gain simple media exposure or governmental manipulation; they want to make an overpowering impact by causing massive loss of life and severe damage to infrastructure and are often motivated by religious imperatives and political goals. As terrorism analyst Stephen Flynn has observed, "Throughout the 20th century [Americans] were able to treat national security as essentially an out-of-body experience. When confronted by threats, [America] dealt with them on the turf of our allies or our adversaries. Aside from the occasional disaster and heinous crime, civilian life [in the United States] has been virtually terror-free." With the turn of the twenty-first century, terrorist operations have become more prevalent in the United States and are taking shape in the form of modern guerrilla warfare, thus creating new challenges for federal, state, and local law enforcement agencies. After reviewing the origin and nature of these challenges, this article will offer some suggestions for countering guerilla warfare in the United States.