["Journal for the Scientific Study of Religion, EarlyView. ", "\nAbstract\nTrust, a cornerstone of economic development, is promoted within religions. In a randomized controlled trial, we examine how trust and trustworthiness vary across religions (Christianity and Islam), religiosity, and atheists/agnostics in the United States. Three novel findings emerge. First, Christians are trusted more than Muslims and nonbelievers, which is due to a Christian ingroup bias––Christians trust Christians more than they trust Muslims and nonbelievers, while Muslims and nonbelievers trust all groups the same. Second, religiosity matters to trust. Religious people trust those of higher religiosity more, but only if they are of the same religion. In contrast, nonbelievers trust people of higher religiosity less. Third, trustworthiness among nonbelievers is somewhat lower than that of the religious, especially toward Christians. We speculate that the lower reciprocity originates in the prejudice toward nonbelievers. Our results may help explain discrimination against Muslims and nonbelievers, given that discrimination often originates in distrust.\n"]