While most explanations of individual trade policy preferences center on the redistributional
implications of trade, recent research is particularly interested in the role of non-economic
determinants. We join the latter line of research by studying the effect of social trust. Our
research breaks new methodological ground by testing the hypothesized causal effect of social trust
in a field survey experiment that combines a voluntary contribution game with a survey. The
empirical work was carried out in Hanoi, Vietnam. The findings offer robust support for the
argument that social trust has a positive causal effect on public support for international trade.