Because fundamental disagreements exist over the definition of terrorism, the United Nations and individual countries have been unable to legislate effectively against it. The modern terrorist generates fear out of all proportion to its results and must be taken seriously by criminal policy planners. The enormous dangers posed by modern terrorists stem from the vulnerability of urbanized society, technological advances which have made weapons of mass destruction available, and enhancement of the terrorist image by the mass media. Terrorism within the United States has been sporadic and has caused little disruption, but Americans are affected by transnational terrorists who have long considered American interests in foreign countries prime targets. Furthermore, the United States can do little to protect its citizens in a foreign country or on international airline flights, although it has refused to negotiate with terrorists in such situations while doing all in its power to provide for victims' safety. Transnational terrorism damages international relations by exploiting ideological differences and placing unreasonable demands on countries where terrorist acts occur. Terrorism appears to have reached a plateau, but new activities with a higher level of destructiveness can be expected since conventional terrorism has ceased to produce its desired effects. Preparations to meet this escalated criminality should be made, such as expanding intelligence activities, improving information exchanges among countries, and establishing lines of communication between private security companies and law enforcement agencies. Some curtailment of traditional liberties, particularly regarding personal privacy, might be necessary to combat high technology terrorism. Groups which are most likely to become involved in escalated terrorism are mercenaries with a nihilistic creed and no expectations of political power, splinter groups forced into a position of desperation, and solitary psychotic imitators. The last category presents the most problems because such persons are unlikely to be detected by intelligence systems. Over 80 footnotes are included.