Muism rarely appears in Korea as a religion competing on equal terms with Buddhism, Confucianism or Christianity for a household's whole allegiance. It runs underneath them instead, addressed for the specific, practical business that the other systems leave less room for: a stalled business, an unexplained illness, a marriage that will not settle, a spirit that has not been sent off properly.
A Korean household across the twentieth century might keep an ancestral rite in the Confucian manner, attend a Buddhist temple or a Christian church on the calendar those traditions set, and still call a mudang, a shamanic practitioner overwhelmingly though not exclusively female, when a problem resisted both. The mudang's central rite is the gut, an elaborate ceremony of music, dance, offerings and possession trance in which she is entered by one or more of a large population of gods, nature spirits and ancestors, speaking and acting as them to diagnose the trouble and negotiate its resolution. The office is typically entered either through hereditary transmission within shaman families, concentrated historically in the south, or through an unsought and often disorienting spiritual crisis known as the shaman sickness, sinbyeong, which initiation into the role is understood to resolve. Laurel Kendall's ethnography of Korean shamanism situates this practice inside real, ongoing household and business life rather than as folklore, which is the frame the atlas follows here: Muism is not a survival being studied, it is a working system some Koreans still call on.