Why do citizens in religious groups and more religious countries give money to charitable causes? In this article we aim to theoretically and empirically unravel the influence of religious composition on giving to non-profit organizations across countries. Building on theories and research in sociology, social psychology, and economics we formulate hypotheses about individual- and contextuallevel differences in engagement in religious and secular charitable giving. We test our hypotheses with multi-level analyses using data from the European Social Survey that include 21 European countries complemented with matching data from the United States (N<inf>1</inf> = 41,314; N<inf>2</inf> = 22). The results show no relationship between country-level devoutness and engagement in religious or secular giving. We do find that citizens in countries with a higher level of religious heterogeneity are more likely to engage in religious giving but not secular giving. We test two explanations for the relationship between giving and religious heterogeneity. We find support for the minority hypothesis that people belonging to a religious minority have a higher likelihood of giving but not for the group size hypothesis that the relative size of the religious denomination to which people belong to decreases their engagement in charitable giving.