Cities are organized through inequality. As sites of both poverty and opulence, they seem to Americans, who have faith in the mass and the middle class, both perverse and fascinating. In the United States we are ambivalent about our cities, evident in our particular patterns of social class settlements ( Beauregard 1993; White and White 1962). Moreover, our choices of residences reinforce inequality. In the United States, most wealthy and middle-class Americans have abandoned the city for the suburbs in an idealized attempt to "control" democracy, escape difference, and reify homogeneity along lines of class and race and patriarchal gender relations. Yet cities are wonderful precisely because of the surprise and challenge that come with the extensive social differentiation and juxtaposition found there: They contain a "mosaic of social worlds" ( Wirth 1938). Our nation's concerns over diversity and inequality seem to be concentrated on the city as a site of social problems: homelessness, ghettoization, gentrification, and the increasing gaps in income and wealth between cities and suburbs. The city is a compelling subject because there is no greater test of our democratic ideals than in the multifaceted metropolis.
Urban research is guided by widespread agreement that urban processes are constituted through uneven development. It focuses on causes and patterns of social inequality and the politics of managing it. Theories of social stratification and urban research have been developed together, since the city, to some degree, contributes to the creation and maintenance of inequalities. Moreover, uban theories reflect upon and inform social reform policies. Below, I discuss how urban research incorporates theories of social inequality. First, I review definitions of social class in urban ecology and political economy, the convergence of a conflict approach with the paradigm shift in urban research, and new debates over polarization and fragmentation in the postindustrial city.