This study explores the consequences and origins of between-ethnicity inequality for a large sample of countries. First, combining satellite images of nighttime luminosity with the homelands of ethnolinguistic groups, we construct measures of ethnic inequality. Second, we uncover a strong inverse association between ethnic inequality and contemporary development above and beyond its relationship with cross-region and cross–administrative unit inequality. Third, we establish that differences in geographic endowments across ethnic homelands explain a sizable fraction of the variation in economic disparities across groups. Fourth, we show that inequality in geographic endowments across ethnic homelands is a negative correlate of development.