Mongolian shamanism, known as the Böö Mörgöl (Бөө мөргөл [pɵː ˈmɵrkʊ̆ɬ]) in Mongolian and more broadly called the Mongolian folk religion or occasionally Tengerism, refers to the animistic and shamanic ethnic religion that has been practiced in Mongolia and its surrounding areas (including Buryatia and Inner Mongolia) at least since the age of recorded history. In the earliest known stages it was intricately tied to all other aspects of social life and to the tribal organization of Mongolian society. Along the way, it has become influenced by and mingled with Buddhism. During the socialist years of the twentieth century, it was heavily repressed, but has since made a comeback.

Yellow shamanism defines a distinct form of shamanism practiced in Mongolia and Siberia. The term "yellow" in "Yellow Shamanism" is derived from "Yellow Buddhist"; more commonly known as Tibetan Buddhism, this style of Shamanism integrated elements of ritual practice and traditional Buddhist customs. The Gelukpa (or Geluk) school of Buddhism, otherwise known as "Yellow Hat", is one of four major schools (Nyingma, Kagyu, Sakya) established by the early 1400s in Tibetan Buddhism. Similar to the other Buddhist schools, Geluk combined the philosophy and cosmology of Mahayana Buddhism and incorporated distinctive qualities from the Vajrayana teachings to develop and cultivate its own traditions. The term Geluk means, "Order of excellence" or "Virtuous order" in the Tibetan language, which reflects the belief in the institution of the Tulku (incarnate lama) unique only to Tibetan Buddhism. Additionally, the color yellow is a significant color in Tibetan Buddhism, as it represents the color closest to daylight and symbolizes the humility Gautama Buddha displayed in choosing a color previously worn by criminals. Another distinctive quality of Tibetan Buddhism are the yellow pandita hats typically worn by monks. The term "yellow shamanism" also serves to distinguish it from a form of shamanism not influenced by Buddhism (according to its adherents), called black shamanism.

Mongolian shamanism revolves around the worship of the "Tngri" (Ancestor spirits) and devotion to "Father sky" otherwise known as "Tenger" or "Qormusta Tengri" in Mongolian. In the Mongolian folk religion, Genghis Khan is considered one of the embodiments, if not the main embodiment, of the Tenger spirit. The Mausoleum of Genghis Khan in Ordos City, in Inner Mongolia, is an important center of this worship tradition.

Mongolian shamanism is an all-encompassing system of belief that includes medicine, religion, a reverence of nature, and ancestor worship. Central to the system are the activities of male and female intercessors between the human world and the spirit world, shamans (böö) and shamanesses (udgan). They are not the only ones to communicate with the spirit world: nobles and clan leaders also perform spiritual functions, as do commoners, although the hierarchy of Mongolian clan-based society is reflected in the manner of worship as well.

Klaus Hesse described the complex spiritual hierarchy in clan-based Mongolian society based on sources that go back to the 13th century. The highest group in the pantheon consists of 99 tngri (55 of them benevolent or "white" and 44 terrifying or "black"), 77 natigai or "earth-mothers", besides others. The tngri are called upon only by leaders and great shamans, and are common to all the clans. After these, three groups of ancestral spirits dominate. The "Lord-Spirits" are the souls of clan leaders to whom any member of a clan can appeal for physical or spiritual help. The "Protector-Spirits" include the souls of great shamans (ĵigari) and shamanesses (abĵiya). The "Guardian-Spirits" are made up of the souls of smaller shamans (böö) and shamanesses (udugan) and are associated with a specific locality (including mountains, rivers, etc.) in the clan's territory.

The difference between great, white and small, black (in shamans, tngri, etc.) was also formative in a class division of three further groups of spirits, made up of "spirits who were not introduced by shamanist rites into the communion of ancestral spirits" but who could nonetheless be called upon for help—they were called "'the three accepting the supplications' (jalbaril-un gurban)". The whites were of the nobles of the clan, the blacks of the commoners, and a third category consisted of "the evil spirits of the slaves and non-human goblins". White shamans could only venerate white spirits (and if they called upon black spirits they "lost their right in venerating and calling the white spirits"), black shamans only black spirits (and would be too terrified to call upon white spirits since the black spirits would punish them). Black or white was assigned to spirits according to social status, and to shamans "according to the capacity and assignment of their ancestral spirit or spirit of the shaman's descent line."

Nationwide reverence of Genghis Khan had existed until the 1930s, centered on a shrine which preserved mystical relics of Genghis, that was located in the Ordos Loop of the region of Inner Mongolia, in China. The Japanese, during the occupation of China, tried to take possession of the relics in order to catalyse a pro-Japanese Mongol nationalism, but they failed.

Within the Mongolian People's Republic (1924–1992) the Mongolian native religion was suppressed, and Genghis' shrines destroyed. In Inner Mongolia, otherwise, the worship of the cultural hero persisted; the hereditary custodians of the shrines survived there, preserving ancient manuscripts of ritual texts, written partially in an unintelligible language called the "language of the gods".