Most studies see demand for populist forces driven by broad sociological factors that make certain issues salient among specific constituencies. However, this argument is not normally tested at the individual level. We propose a theory of populist voting which argues that populist attitudes are themselves important predictors of voting, interacting with ideological positions. We test this theory through a comparison of recent voting in Chile and Greece, two countries where the contexts for activating populist attitudes are very different. We find that despite similar levels of populist attitudes across both countries, these attitudes explain much more of the vote in Greece than they do in Chile, and that in both countries they interact with ideological positions in predictable ways.