A literature review indicates that hypnosis can be measured reliably. The various predictors include general S-variables, test variables, and personality variables. There are no cross-validated predictors and little positive correlation between the common personality and S-variables. Consequently, hypnotizability may be an independent variable. A two-factor hypothesis is suggested, tranceability, the ability to have hypnotic experiences, and a non-ability factor composed of needs, motives, and attitudes toward hypnosis.