This heading names a scholarly category, not a religion, and the category is contested enough that it should be dealt with first.
The word comes from saman in Evenki, a Tungusic language of eastern Siberia. Russian officials and travellers picked it up in the seventeenth century, applied it across northern Asia, and by the nineteenth century European writers were using it for ritual specialists in the Americas, Africa, Southeast Asia and Australia. Mircea Eliade's book of 1951 completed the move, defining shamanism as archaic techniques of ecstasy and treating it as a single worldwide phenomenon with a common structure of trance, soul flight and a layered cosmos.
That framework shaped a great deal of subsequent writing and has been substantially picked apart. Alice Kehoe has argued that generalising a Siberian word to unrelated practices produces a category that describes European expectations rather than anything the practitioners share, and that it flattens genuine differences while carrying an implication of primitiveness. Andrei Znamenski has traced how the shaman was constructed in Western imagination, first as a fraud or a psychiatric case in the eighteenth and nineteenth centuries, then as a figure of spiritual wisdom from the 1960s, with the evidence bending each time to the fashion.
Within Siberia itself the objection has force too. The peoples grouped here (Evenki, Buryat, Sakha, Tuvan, Khakas, Nenets, Chukchi, Nivkh and others), speak languages from several unrelated families and differ in cosmology, in the terms they use for their specialists, in how those specialists are recruited, and in what they are for. Buryat and Tuvan practice is deeply entangled with Tibetan Buddhism; Sakha tradition distinguishes categories of practitioner that do not correspond to the single figure of the model.
The grouping remains useful as a rough regional heading, and is used that way here. It should not be read as a claim that these peoples share one religion.