This thesis is concerned with the intractability of adult obesity for hypnotherapy and is presented in two parts the first being concerned with the nature of the problem and the second with developing a solution. The thesis first considers the impact of adult obesity on the English economy and National Health Service. The limited response of the National Health Service is examined and a review of evidenced-based (non-surgical or pharmacological) interventions in obesity is carried out. The general intractability of adult obesity is investigated with regard to the misguiding influence of the energy balance equation and psychological issues including the implications of food-related attitudinal ambivalence. Determination of the nature of the problem concludes with an historical overview of hypnotherapy for adult obesity prior to an examination of the evidence for hypnotherapy in adult obesity and of factors which may diminish its effectiveness. The second part of this thesis reports the development of a system of confidential IMR based one-to-one hypnotherapy in a group setting as a means of reducing treatment costs for adult obesity for patients from lower socioeconomic groups, where the condition is most prevalent. In addition the system provides a facility to treat food-related attitudinal ambivalence which is reasoned to result in resistance to hypnotic suggestions aimed at stopping hyperphagia. Inferential analysis conducted during the empirical part of the study has shown that the new one-to-one hypnosis in a group setting is no less effective than normal group hypnosis. Further limited inferential analysis suggests that the new system of hypnotherapy was instrumental in generating improvements in a range of psychological, behavioural and biological variables associated with participants' hyperphagia. This work contributes to hypnotherapeutic knowledge and practice by the conceptualization and development of one-to-one hypnotherapy in a group setting and the facility to treat food-related attitudinal ambivalence.