The present article analyzes the September 11 terrorist attack on the World Trade Center and the Pentagon in terms of current theories of normative influence in intergroup conflict. The (conflicting) implications of various social psychological models of decision making for Western and American attempts to reduce the likelihood of further attacks are delineated. We examine the implications of social identity models and models of outgroup normative influence, as well as dynamic models of intergroup behavior that focus on the polarizing effects of outgroup hostility. The influence of Western responses is distinguished for various target audiences, including not only the terrorists, but also pro-Western Muslims in North America and Europe, unaligned Muslims, and Muslims with anti-American feelings who do not endorse terrorism.