Why do some ethnic groups vote along ethnic lines while others do not? In this article, we theorize that the level of ethnic voting depends, partially, on how ethnicity interacts with economic cleavages. Specifically, we argue that between- ethnic group inequality (BGI) increases ethnic voting and that its effect strengthens as within-ethnic group inequality (WGI) decreases. We thus posit that the full structure of ethnic inequality, not only between-group differences, matters for ethnic voting. After presenting our argument, we conduct the first cross-national test of whether the effect of between-group inequality on ethnic voting is conditional on the level of inequality within ethnic groups. Our analysis employs group-level data on 200 ethnic groups from 65 countries. We find strong support for our hypothesis: BGI increases ethnic voting, but its effect is conditional on WGI.