Significant levels of separation between blacks and whites still exist in large American cities, and debate about the causes of that residential separation has been considerable. A balanced analysis of the factors that might explain residential segregation -economic status (affordability), social preferences, urban structure, and discrimination -suggests that no one factor can account for the patterns that have arisen in U.S. metropolitan areas. Empirical estimation of the impact of economic status suggests that 30-70 percent of racial separation is attributable to economic factors. However, economic factors do not act alone, but in association with preferences. Together with elements of the urban structure, these factors bear much of the explanatory weight for present residential patterns. Survey evidence from both national and local studies shows that black households prefer neighborhoods that are half black and half white, while whites prefer neighborhoods ranging from 0 to 30 percent black.The debate about causes seems most polarized over the role of discrimination. Although comments in the literature often focus on the past use of racially restrictive covenants by stateregulated agencies and discriminatory acts by realtors and financial institutions, the documented individual cases of discrimination do not appear to be part of a massive collusion to deny housing opportunities to minorities. A review of the evidence from social science investigations demonstrates that there are multiple causes of racial residential separation in U.S. metropolitan areas.