The study drew upon a literature review from libraries in Washington, D.C., and information from the Rand Corporation's data base on existing terrorist organizations. Interviews were conducted with terrorism scholars, the police, and counterterrorist agencies throughout the world. Distinguishing between political crime and common criminality involves a process of negotiating over definitions based on ideology, power, and claims and defenses of legitimacy demonstrated by such criteria as characteristics of group members and victims. At the extreme, political terrorism can become gangsterism involving serious, violent common criminal activities and the entrance of common criminals into the organization. Such a pattern may entail a change in the group's ideology in terms of the aims and justification of its activities. Common criminals, as opposed to political terrorist, try to avoid publicity. Although both terrorist and common criminals may target individuals, groups, or property, some terrorist groups in certain stages of their development (small, weak, marginal, and unknown) may use indiscriminate victimization to gain publicity. Official responses to terrorism are to either label it common criminality, or in the case of a guerrilla army with 'liberated zones' to label terrorist violence as civil war. The paper concludes with a listing of some examples of the static and dynamic relations between political terrorism and common criminality.