This analysis brings the many resources of psychological science and practice to bear on the problem of terrorism by providing empirically-based theory and interventions for understanding, intervening and preventing this challenge to international security. It addresses many of the conceptual and definitional issues associated with terrorism, especially those arising from the complex historical and cultural variations in its meaning, motives and consequences. Terrorism, by definition, attempts to change the psychological state of its targets, so psychologists are well-positioned to cast light on this phenomenon. In this work, international experts offer an analysis of the psychosocial basis of terrorism and suggest ways to prevent it, including both strategies to eliminate the conditions that give rise to terrorism as well as effective ways to treat victims of terrorism.