Obesity is one of the biggest public health issues in the United States. Approximately one third of the U.S. population are obese, and another one third are overweight, putting them at risk of developing obesity in the future. There are a number of treatments for excess body weight; however, most are limited by the amount of weight loss they produce and the problem of weight regain over time. Treatment success also can be limited by a number of psychosocial and behavioral factors. After further defining obesity and discussing the obesity problem and its causes, this entry focuses on the various treatment options as well the role of the mental health professional in obesity treatment.