This article reviews the origins of the concept of the shaman and the principal sources of controversy regarding the existence and nature of shamanism. Confusion regarding the nature of shamanism is clarified with a review of research providing empirical support for a cross-cultural concept of shamans that distinguishes them from related shamanistic healers. The common shamanistic universals involving altered states of consciousness are examined from psychobiological perspectives to illustrate shamanism’s relationships to human nature. Common biological aspects of altered states of consciousness help explain the origins of shamanism while social influences on this aspect of human nature help to explain the diverse manifestations of shamanistic phenomena involving an elicitation of endogenous healing responses.