To increase understanding of global variation in contraceptive use, we classify countries into "cultural zones" based on religious traditions and geographical regions. Using data for 156 countries, we model modern contraceptive use rates as a function of cultural zones, geographic regions, economic development, women's education, and time. We find that cultural zones explain modern-method contraceptive use better than geographic regions alone, even when adjusting for economic development, women's education, and time. We argue that practitioners and researchers should make use of cultural zones as a tool for understanding cross-national variation in sexual and reproductive health outcomes.