This essay suggests that 9-11 constitutes a critical event for urban scholars because it encapsulated & catalyzed a trend toward urban-based terror that had been building for over a decade. The author argues that the best way to put 9-11 in perspective & understand its significance is through a paradigm, & suggests a set of components that set the parameters for explanation. These consist of the diffusion of terror as an urban phenomenon, the economic ramifications of urban terror, & the impact of terror on the use of urban space. (63 refs)