Since the 1920s, the discourse about American urban culture has suggested the appropriateness of organizing metropolitan life around territorial subcommunities in two distinctive ways, each of which yielded a distinctive period in the history of professional city and social welfare planning. During the first period, which persisted into the 1950s, the planners focused on the problem of forging a coherent sense of metropolitan community among cultural groups conceived of as separate but equal (or potentially equal). To achieve this goal, they emphasized the role of experts in analyzing the forces controlling urban culture and in devising schemes to segregate, assure the integrity of, and foster mutual understanding and respect among cultural groups whose characteristics stemmed from forces beyond the control of experts or group members. During the second period, which began in the 1950s and persists in our own time, planners abandoned cultural group determinism and the quest for a segregated yet coherent metropolitan community of separate but equal groups in homogeneous neighborhoods. Instead they decided they could control the future of the metropolis by persuading individuals to create heterogeneous neighborhoods through a process of “community action” in which neighborhood residents would define their culture (“lifestyles”) by participating in the design of the social and physical environment of the neighborhood of their choice. This new pattern of thinking about urban culture, which centered on “individualism” and neighborhood rather than groups and metropolitan community, involved a revolt against cultural group determinism, the notion that individuals carry an identity determined by the accident of their membership in the group with characteristics determined by the experience of a group in a social and physical environment created by “outsiders” and or impersonal “forces.”