In this paper, we examine religiosity as one determinant of tax avoidance by corporate and individual taxpayers. Prior research suggests a relation between religiosity and risk aversion. Because aggressive tax avoidance strategies involve significant uncertainty and possible penalties and damage to reputation, we predict that higher levels of religiosity are associated with less aggressive (i.e., less risky) tax positions. Consistent with this prediction, we find that firms headquartered in more religious U.S. counties are less likely to avoid taxes. We also find that religiosity is consistently associated with lower tax avoidance by individual taxpayers, as measured by underreported income. These results hold after controlling for several firm-level, as well as county-level, demographic characteristics identified in prior research as affecting tax avoidance by corporate and/or individual taxpayers. We conclude that religiosity is a significant determinant of tax avoidance by corporate and individual taxpayers.