Drawing on the strategic surprise, warning-response, and foreign policy literature, this article argues that the September 11 terror attacks should be regarded as a strategic surprise and examines a number of key factors that contributed to vulnerability and inhibited vigilance. Three broad explanatory ‘‘cuts’’ derived from the literature—psychological, bureau-organizational, and agenda-political—are deployed to sift through the rapidly expanding empirical record in an effort to shed light on the processes and contextual factors that left the United States vulnerable to the attacks. The article aims to improve our understanding of generic processes and practices that enhance or detract from vulnerability and vigilance.