This article uses a political market framework to analyze how the structure of local political institutions affects the relative political influence of development and environmental interests in the context of urban growth. Using panel data from 406 Florida cities from 1998 to 2003, the empirical analysis finds important interaction effects between the structure of city executive branch institutions and interest group variables. The economic and political forces driving urban growth do not operate identically in all cities—they vary as a function of institutional context. Institutional structure helps determine which interest groups have their preferences reflected in local land-use changes and development patterns. The resulting patterns suggest a “sustainability paradox” wherein richer, environmental interests push for the preservation of environmental amenities while at the same time accelerating the number of residential units built in a community.