Diffuse urban development is the most pervasive, desired, and yet socially controversial form of city making. This built environment, increasingly described as "exurban," is characterized by large-scale, low density and poorly defined fragments, scattered across metropolitan territories. In North America, the original postwar suburban sections of this environment are up to 70 years old, suffering from material decline as well as functional, spatial, and social detachment and are at the end of their first life. This positions them well for cultural and spatial renewal in ways that embrace changing social, political, and economic circumstances. The challenge for architects, planners, and civic leaders is to imagine and design such a conversion in ways that allow for functional complexity, social interaction, and cultural diversity. For more than three decades, recent immigration from Asia and Latin America have brought new values and related spatial practices to aging postwar suburbs. Most visible in California and Arizona, these cultural adaptations of an iconic built environment provide new insights into the future form of the exurban city, one that is set to develop through a much different set of priorities and related design techniques. Such a vibrant and compelling altered world will emphasize increased residential density, functional complexity, and social interaction. The predicted changes in the basic zoning codes of our maturing exurban cities will better accommodate and illustrate new and diverse values and customs in ways that benefit all residents of the contemporary polycentric city.