There is now widespread recognition among urban researchers that a fundamental shift is underway in the internal structure of American urban areas. Polycentrism is increasingly supplanting monocentrism as the dominant urban form. However, the extent to which this has occurred and the implications of this change in urban form, while widely noted and discussed, have, surprisingly, not been the subject of a large body of carefully conducted and generalizable empirical research. We explore the extent of polycentrism for a sample of fifty U.S. metro areas, using an absolute threshold definition for identifying employment centers. We situate our results within the broader literature on subcenters, and compare our results to previous research on
polycentrism. Using cluster analysis, we identify broad types of metros according to the incidence and patterning of centers within our sample. Variables of interest include the number of centers, the relative concentration of jobs within centers, the relative dominance of the core center, and the concentration of employment in major and minor centers. We also explore relationships between types of polycentrism and various metro attributes, such as population size, city age, geographic region, municipal fragmentation, and economic function. Finally, we set out a detailed agenda for future research.