Study data came from a review of literature focusing on a variety of types of terrorism and examining psychological traits, sociological rationales, historical trends, and terrorists' stated views. Findings showed that no consensus exists regarding the definition of a terrorist, a terrorist act, or a terrorist group. Most writers group terrorists into three broad categories: the idealist, the political radical, and the person with mental problems. Most writers also conclude that motivation varies widely among different terrorists. Many terrorists were involved with nonviolent movements before joining the terrorist group. Many terrorists were students. Some experienced rejection by parents, teachers, or their peer group. Others were susceptible to writings or even teachers. Some groups are formed and directed by a single leader; others have been trained and organized under Soviet influence. Most groups lack clearly defined goals. Groups require publicity for their existence. Groups also have several vulnerabilities, particularly their constant tension. Finally, much of the writing about terrorism lacks scholarly thought or empirical data. Notes and 34 references.