This monograph covers the medical, psychological and biological features of bariatric surgery. From a multidisciplinary view, important aspects both before and after bariatric surgery are considered. Firstly, this monograph focuses on the evaluation of bariatric surgery candidates, both considering the pathology and psychopathology of morbidly obese patients. Also, special attention is given to measurement instruments applied during the psychological assessment of these patients. Secondly, surgical techniques used in bariatric surgery are covered. A detailed description of these techniques, also considering their possible postoperative and late complications is provided. A comparison of long-term results obtained by the different surgical techniques is also included. Other features related to surgical intervention, such as revision surgery or plastic surgery are also covered. Thirdly, a chapter about bariatric surgery in adolescents has been included. Specific guidelines and considerations of the application of bariatric surgery to adolescents are discussed. Another aspect that is covered in the present publication are metabolic changes in morbidly obese patients, both before and after bariatric surgery. A description of changes in carbohydrate and lipid metabolism, satiety factors and other metabolic parameters involved in morbid obesity are also provided. Adherence to dietary recommendations is also considered. Dietary recommendations before and after bariatric surgery, and cognitive and behavioural techniques that promote their adherence are provided. Finally, the impact of morbid obesity on health-related quality of life, its improvement after bariatric surgery and the therapeutic approach to improve quality of life among these patients is included.