We study the role of social trust in the equity allocation decisions of global investors using a large sample of institutionally managed portfolios of 8,088 investors from 33 countries over the 2000 through 2017 period. The negative relationship between social trust and foreign bias suggests that institutional investors from high-social trust countries are less prone to underinvesting in foreign equity. Our results provide credence to an information-based explanation, indicating that social trust reduces foreign bias by compensating for the lack of information about foreign stock markets. Moreover, the effect of social trust on foreign bias is stronger if host-country institutions are weak, while it vanishes when the host country is characterized by strong institutions. The informal institution of social trust compensates for the lack of well-functioning formal country-level institutions in international portfolio decisions. Finally, the allocation effect resulting from social trust is different from “blind” trust. The portfolios of high-trust investors exhibit higher cross-country diversification and an enhanced portfolio risk-return trade-off.