The shaman is the specialist in non-ordinary reality — the trained practitioner who can deliberately enter altered states of consciousness and travel to the spirit world to retrieve information, power and healing for individuals and the community. This role is found in virtually every pre-agricultural and indigenous culture in human history, making it arguably our species' oldest spiritual technology.
The core shamanic understanding is that reality has multiple layers — an ordinary reality of physical existence and a non-ordinary reality of spirit, where different laws apply and where the roots of both illness and healing can be found. The shaman's ability to move between these realities — and to bring back useful knowledge and power from the journey — is the defining feature of the tradition.
Historian of religions Mircea Eliade, in his landmark 1951 study "Shamanism: Archaic Techniques of Ecstasy," identified the core techniques as remarkably consistent across cultures: the shamanic journey induced by percussion (primarily drumming), the concept of spirit helpers or allies, the three-world cosmology (upper, middle, lower) and the shaman's role as intermediary between the human and spirit worlds.
What distinguishes the shaman from other spiritual practitioners is the deliberate, controlled entry into altered states for specific purposes — unlike the mystic who seeks union with the divine, the shaman travels to the spirit world, completes a task and returns with the results. The shaman's ecstasy is purposeful and disciplined.