The article describes different types of terrorists including criminal, psychopathic, subrevolutionary and revolutionary terrorists; the outtlook for further terrorist activity; and various causes of terrorism such as resistance to colonial rule, the desire to create a splinter state from an existing one, assumption of State power, destruction of an ideological system of government, and the conquest of another Nation - State. Revolutionary terrorists always work in groups, support a leader and an ideology, create institutions such as folk legends and a collective personality, acquire weapons and training, and maintain secrecy. Leaders of these groups are usually pragmatic, power-oriented Marxists. Activist-operator members who carry out the group's activities are usually less intelligent, undereducated, and trained in violence (either in the military or as criminals). Idealists supporting the group are generally young, alienated, and educated, and represent the largest proportion of the group. Terrorists among various industrialized countries are similar in background, education, and in the route they take to joining a terrorist group. Terrorist groups in all these countries include a significant proportion of women. Members of radical student organizations follow a standard path from legal dissent, such as peaceful demonstration, to illegal and violent dissent practiced by terrorists such as assassination and sabotage. Terrorist roles include specialist and direct supporters and a hard core of leaders and basic action participants. Upper and middle-class youth compose the largest portion of terrorist groups. They become alienated from parental lifestyles due, possibly, to pressure to achieve, a lack of parental attention, or models promoted by parents for protesting social injustice. Countries who react to terrorism often fail to allow for the extensive preparation which terrorists engage in, underestimate the threat which they represent, provide a slow response, react with inadequate measures, and appear indecisive. Effective countermeasures include eliminating sanctuaries, protecting targets, improving detection, and strengthening the court system. In addition, terrorists tend to unite under pressure, to grow weaker during idleness, and to generate their own internal momentum. They may serve the group rather than serve the cause and may become ends in themselves. Terrorist group problems include size limitation, their tendency to escalate their targets and to lose public support, and political problems caused by questions over what should be done after the target government has been eliminated. Terrorism will probably continue in the future, although new target Nations and types of action will probably develop. Thirteen figures are included.