This paper provides a comparative assessment of income segregation within cities in 12 countries. We use spatial entropy indexes based on small-scale gridded income data and consistent definition of city boundaries to ensure international comparability of our segregation measures. Results show considerable variation in the levels of income segregation across cities, even within countries, reflecting the diversity of cities within urban systems. Larger, more affluent, productive, and more unequal cities tend to be more segregated. Urban form, demographic, and economic factors explain additional variation in segregation levels through the influence of high-income households, who tend to be the most segregated. The positive association between productivity and segregation is mitigated in polycentric cities.