Use encyclopedias etc for introductions to or brief summaries of topics in religion:
Encyclopedia of ReligionThe second edition of a resource that is considered a standard reference in the field. Presents a cross-cultural approach that emphasizes religion's role within everyday life and as a unique experience from culture to culture.
Encyclopedia of World Religions - Encyclopaedia BritannnicaA guide to the religions of the world and to the concepts, movements, people, and events that have shaped them. It includes features such as: entries on religious movements and concepts, historical and legendary figures, divinities, religious sites and ceremonies; images that show sacred places, vestments, rituals, objects, and texts; and more.
Association of Religion Data Archive (ARDA)This link opens in a new windowData on religion around the world, with a primary focus on the United States. Interactively generate national profiles, maps, church membership overviews, and other summary reports. Covers since the archive began in 1997, with some data sets including earlier sources.
Buddhism - Oxford BibliographiesThis link opens in a new windowProvides authoritative research guides that combine an annotated bibliography and a high-level encyclopedia. Includes both classic and contemporary research covering the entire range of Buddhist history, thought and practice.