Milton Erickson is the most famous contemporary hypnotherapist, as well as a legendary psychotherapist. At the age of seventeen, he narrowly escaped death from poliomyelitis, but continued to suffer from residual paralyses that worsened later in his life. This chapter relates how such experiences taught him the power of the unconscious mind and the trance state, and led him to pursue a career in hypnotherapy and psychotherapy. It also discusses Erickson’s view on trance, his relationship with Margaret Mead and Gregory Bateson, and his influences on a new generation of innovative psychotherapists. Also covered are discussions on the nature, origin, and importance of the “altered state of consciousness,” the importance of such phenomena vis-à-vis the evolution of our species, as well as the role “altered state of consciousness” has played in the history of psychiatry.