The urban geography literature emphasizes differences in cities’ street network forms, but this talk argues that, in many ways, they exhibit remarkable universality across cities. We model the street networks of every urban area in the world and calculate street network form indicators, then compare the statistical dispersion of these indicators with that of other urban characteristics unrelated to network form. Despite vast differences in geography and planning history, cities converge on a consistently narrow and homogeneous set of street network forms—a phenomenon we do not see for city size and other urban characteristics—across cities of drastically different origins and planning paradigms, which we argue is due to specific urbanization processes, physical constraints, and optimization.