Three types of hypnosis are discussed: stage, therapeutic, and criminal. The article emphasizes that persons being hypnotized have complete control of themselves at all times and are aware of their environment. A case is described in which hypnosis helped the recall of a woman who witnessed her husband being taken away by two suspects. Hypnosis was used a second time to prevent trauma when she was told of the recovery of her husband's body. The article emphasizes that hypnosis, like the use of the polygraph, is a tool and that findings need corroboration. It also briefly explores the limits of hypnosis for some subjects, pain and hypnosis, and study and hypnosis. Some sources of information are listed.