This article reviews the state of the art of available theories and data regarding the psychology of terrorism. Data and theoretical material were gathered from the world's unclassified literature. Multiple theories and some demographic data have been published, but very few controlled empirical studies have been conducted investigating the psychological bases of terrorism. The field is largely characterized by theoretical speculation based on subjective interpretation of anecdotal observations. Moreover, most studies and theories fail to take into account the great heterogeneity of terrorists. Many practical, conceptual, and psychological barriers have slowed progress in this important field. Nonetheless, even at this early stage of terrorism studies, preliminary reports suggest that modifiable social and psychological factors contribute to the genesis of the terrorist mind-set. Psychological scholarship could possibly mitigate the risk of catastrophic attack by initiating the long overdue scientific study of terrorist mentalities. (Contains 3 tables and 1 figure.)