Hypnotherapy is therapy that is undertaken with a subject in hypnosis.

The word “hypnosis” is an abbreviation of James Braid’s (1843) term “neuro-hypnotism”, meaning “sleep of the nervous system” However, Braid himself rejected the term “hypnosis” as misleadingly implying a similarity between “hypnosis” and normal sleep. He later attempted to substitute a new terminology by referring instead to “ideism” or “monoideism”, an application of the physiological mechanism known as the “ideo-motor response.” The ideo-motor theory of suggestion became influential, however, the old terminology of “hypnotism” remains popular to this day.

A person who is hypnotized displays certain unusual characteristics and propensities, compared with a non-hypnotized subject, most notably hyper-suggestibility, which some authorities have considered a sine qua non of hypnosis. For example, Clark L. Hull, probably the first major empirical researcher in the field, wrote,

If a subject after submitting to the hypnotic procedure shows no genuine increase in susceptibility to any suggestions whatever, there seems no point in calling him hypnotized.

Hypnotherapy is often applied in order to modify a subject’s behavior, emotional content, and attitudes, as well as a wide range of conditions including dysfunctional habits, anxiety, stress-related illness, pain management, and personal development.