Terror and terrorism require a perpetrator, a victim, and an observer or audience; and signify strategic, deliberate, and purposeful aggression carefully timed for audience reaction. Both terror, inflicted from above by the powerful on the powerless, and terrorism, imposed from below by the powerless to intimidate the powerful, operate on the manipulation of fear. The intrinsic mutual dependency of terrorism and mass media contributes to making terrorism a fast spreading growth industry, since without the possibility of notoriety and hence contagion, terrorism could not flourish. Terrorists can be emotionally disturbed; criminal, using terrorism for personal gain; or crusading--idealistically inspired. Terrorists' actions are characterized by unpredictability and seeming senselessness. Causes of terrorism are rooted in the idea of remediable injustice and in the ability of a terrorist group to offer a unifying identity conferring worth, belonging, and meaning to an individual, whereby the individual can gratify his most elementary, infantile, and grandiose desires for omnipotence or aggressive release. What is needed is the prompt relief from remediable injustice, the availability of credible nonviolent conflict resolution, and the possibility for voicing grievances. To achieve these goals, behavioral scientists should contribute to innovative social planning and intuitive social experimentation. Psychiatrists should educate police, media, and public representatives about the dangers in terrorism's contagion and attraction so that these professionals themselves, avoid adopting terrorist tactics. Eight references are provided.