Recent research finds that voters do not have economically self-interested preferences about trade policy. This article investigates one potential explanation for this puzzling finding: economic ignorance. We show that most voters do not understand the economic consequences of protectionism. We then use experiments to study how voters would respond if they had more information about how trade barriers affect the distribution of income and the economy as a whole. We find that distributional cues generate two opposing effects: they make people more likely to express self-serving policy preferences, but they also make people more sensitive to the interests of others. In our study both reactions were evident, but selfish responses outweighed altruistic ones. Thus, if people knew more about the distributional effects of trade, the correlation between personal interests and policy preferences would tighten. Citizens in our experiments also responded strongly to information about efficiency. When we presented the classical case for free trade, support for protectionism fell sharply, the correlation between personal interests and policy preferences weakened, and the gender gap in protectionism disappeared. These findings provide a foundation for more realistic, behaviorally informed theories of public opinion and international trade.