Increasing laboratory and clinical research during the past 25 years has greatly enhanced understanding of hypnosis. Drawing on this research, the authors illuminate the many factors that define the domain of hypnosis, the most crucial of which is individual differences in hypnotizability. The important treatment ramifications of this factor are discussed, as are its pathogenic and diagnostic possibilities. The authors examine hypnotizability from a developmental perspective and conclude with an in-depth discussion of the clinical use of hypnosis with children, who have been shown to be particularly susceptible to hypnotic suggestion.