It has been long contended that terrorism is a form of psychological warfare with the aim of advancing political objectives through the spreading of fear. The present set of five studies explored the relation between need for closure and the social response to terrorism. We found support for the notion that reminders of terrorist attacks elevate the need for closure and that the need for closure may enhance ingroup identification; interdependence with others; outgroup derogation; and support for tough and decisive counterterrorism policies and for leaders likely to carry out such policies. The implications of this research for the claims of terrorist ideologues regarding the efficacy of terrorism are discussed.