What are the sources of popular opposition to economic globalization? A common answer in the literature is the adverse impact of trade liberalization on some people's labor market standing and earning prospects. Recent studies also note a correlation between nationalist and ethnocentric sentiments and support for trade protectionism, yet do not test whether these non-economic sentiments are actually a cause of the opposition to freer trade. I argue that many individuals fear not only the oft-cited material consequences of trade openness, but also what they perceive to be its social and cultural consequences. I use cross-national survey data and a survey experiment to test this causal claim. The argument also helps explain why less-educated individuals are consistently more apprehensive about international economic integration than more educated individuals, even in the countries in which economic theory predicts otherwise. The findings have implications for the debate over the policy tools for compensating globalization's losers and sustaining popular support for further economic integration.