Is religion more of an integrative or a divisive force in contemporary societies? We use multilevel analyses of World Values Survey data from 77,409 individuals in 69 countries to examine how both the percent of the population that is religious and the religious heterogeneity of a country are related to generalized social trust, the willingness of individuals to trust “most people.” When we first examine the main effects of the percent religious and religious heterogeneity we find no evidence that either variable is related to trust in the ways predicted by major theories. However, the combination of these two variables has a huge negative relationship with trust. Countries that are both highly religious and religiously heterogeneous (diverse) have, on average, levels of trust that are only half the average levels of countries with other combinations of these two variables. The results have important implications for understanding the role of religion in modern societies.