Religion is complex in Beijing, and in China in general. Many of the belief systems hover somewhere between traditional religion and old philosophy, as they universally believe in a sacred or spiritual world, but vary in how influential that world is in everyday life. Religions in China also do not demand exclusivity from their members. Chinese citizens may practice several different religions at one time, without feeling any sense of disloyalty.
That said, there are three main religions (or philosophies as the case may be) prominent in Beijing culture: Buddhism, Daoism, and Confucianism. Daoism (also called Taoism) is the only one native to China. Islam and Christianity have made minor inroads into the city.