The municipal zoning process in the United States has come under increasing attack as a tool to create and maintain suburban socioeconomic homogeneity by mandating sprawl-producing single-family detached houses at the expense of less costly townhouses, apartments, and mobile homes. Beginning in the 1970s, the Supreme Courts of the neighboring states of Pennsylvania and New Jersey addressed municipal exclusionary zoning in different ways: Pennsylvania empowered residential developers to compel municipalities practicing exclusionary zoning to authorize market-rate development of all types of housing, while developer empowerment in New Jersey was conditioned upon inclusion of low- and moderate-income units. Using aerial survey and housing census data over a 20-year period, this article finds that outcomes by housing type over a 20-year period in Pennsylvania municipalities around Philadelphia were more diverse than those in adjacent New Jersey municipalities. © 2004 by the Association for Public Policy Analysis and Management.