Using an innovative methodological approach combining field experiments, case studies, and statistical analyses, this book explores how the religious beliefs and institutions of Catholics and Muslims lead them to be generous with their time and resources in order to sustain their religious organizations and to help others. The authors use data from research involving more than 1000 Catholics and Muslims in France, Ireland, Italy, and Turkey. Based on theories from political science, social psychology, economics, and religious studies, this approach provides an understanding of the causal mechanisms that may enable religious communities, situated within particular sociopolitical contexts, to prompt generosity and goods provision. The authors provide insight into what different religious beliefs mean to Muslims and Catholics, how they understand those concepts, and how this affects their behavior.