Research into third wave and/or mindfulness interventions (TWM) has developed greatly over the last two decades, with much research illustrating the benefits of these approaches on a multitude of psychological and physical health problems. Chapter one of this thesis is a systematic review investigating the effectiveness of TWM on weight self-stigma, body image, and body weight in individuals with overweight/obesity. A systematic search of electronic databases was carried out and a total of 12 experimental studies met the inclusion criteria. Data from these papers were compiled and synthesised into a narrative review. The overall pattern of results suggested that TWM interventions may reduce weight self-stigma and improve body image. Results were less clear for body weight. Results should be interpreted with caution due to limitations such as non-generalisability and risk of bias in the included studies. The discussion suggests the need for more rigorously designed trials with diverse populations. Chapter two investigates the relationships between weight stigma, body image and excess weight loss (EWL) and the moderating effect of the TWM self-compassion. Participants in this cross-sectional study had undergone bariatric surgery at one of three National Health Services (NHS) within the last 5 years (n = 87). They were predominantly female (88.5%), White British (90.8%) and aged over 45 (55%). Participants completed a battery of self-report questionnaires via online survey. Results showed self-compassion was associated with better body image. The relationship between internal stigma and body image was moderated by self-compassion, such that for participants with high self-compassion, their appearance evaluation was dependent on their level of internal stigma, whereas participants with lower levels of self-compassion evaluated their appearance poorly irrespective of stigma. Stigma and body image were not associated with EWL. This thesis suggests that TWM, particularly those increasing self-compassion, in bariatric surgery candidates could be a helpful intervention to improve outcomes from surgery.