While debates continue about the relationship between state-provided social welfare and religious charities, and whether organized religions are more capable of providing social welfare than is the public sector, less attention has focused on the question of what motivates religious adherents to contribute to the charitable work of their religions. In this article, we examine how adherents of Catholicism and Islam understand their generosity and its relationship to their faith. Through 218 semi-structured interviews with Catholics and Muslims in four cities in France, Ireland, Italy, and Turkey, we find systematic differences between the two religions. Catholics emphasize love of others and Muslims emphasize duty to God. We also find, contrary to expectations of the literature that emphasizes monitoring and sanctioning within groups to obtain cooperation, that Catholics and Muslims see their generosity as also motivated by the positive affect they feel towards their respective communities.