As far back as the historical record goes, shamanism was the oldest religion practiced in Asia, which was once a single cultural area extending over Russia, China, India, Mongolia, Tibet, Nepal and Persia; where shamanism was concerned, these were a unified culture.

 From this original shamanism comes Siberian shamanism (suppressed by the Soviets, but now making a comeback in the Buryat republic), the Bon religion, and probably Chinese ancestor-worship (?). Buddhism spread throughout central Asia after 600 BC; Tibet converted from Bon to Buddhism about 800 AD; Tibetan Buddhism - usually called lamastic Buddhism - embraced most of the elements of Bon and also of Indian tantrism . . . becoming, essentially, a shamanistic religion. Tibetan lamas fall into trances, predict the future, and in many important ways behave exactly like shamans. After 1300 AD, the Mongols converted from shamanism to lamastic Buddhism, and this faith spread all the way up into Siberia.

Early Mongolian contacts with Buddhism are dated to the fourth century, when the activities of Chinese monks among the population of this border area are reported in contemporary Chinese sources. Buddhist influences spread as far as the Yenisei region by the seventh century, as evidenced by Buddhist temple bells with Chinese inscriptions found there. Another factor in the spread of Buddhism into Mongolia was the flourishing of Buddhist communities in the predominantly Uighur oasis states along the Silk Route. Furthermore, the palace that was built by Ogedei Khan (1229-1241) in Karakorum, the Mongol capital, was constructed on the foundations of a former Buddhist temple; some of the murals from this temple have been preserved, Sources for this early Buddhist activity are rather scarce.

Christians in Mongolia are considered a minority group. Accounts of the exact number of Christians vary as no nationwide statistics have even been released. In 1991 there were 0 christians, any numbers since them resulting from missionary work, mainly originating in the US. As of 2005, the United States Department of State reports that approximately 24,000 Christians live in Mongolia's capital, Ulaan Baatar, which is around 3 percent of the entire registered population of the city. In reality many coverts lapse after a few years, due to the lack of a christian tradition in Mongolia and the lack of cultural awareness of many missionaries.

In Mongolia today, there is a significant minority of Sunni Muslims, constituting as much as 5% of the total population. Most of them are ethnic Kazaks who live primarily in the far western aimag of Bayan-Olgii (there is also a small Kazak community in and around Nalaikh, near Ulaanbaatar).