The rapid increase in the prevalence of obesity over the past few decades has attracted much interest by economists about its cause, but far less interest in its economic consequences. Of particular importance is the question: who pays for obesity? In this report, I review the contribution that my colleagues and I have made toward answering that question. Many people have argued that the rising prevalence of obesity over the past decades is socially expensive because the obese consume more medical resources than thinner people. While it is certainly true that obesity is the cause of, and is associated with, many conditions that are expensive to treat, it does not logically follow that obesity is socially expensive. The true social costs of obesity depend upon the extent to which obese individuals impose costs on others, costs that they do not take into account when they do things that affect their body weight. Yet despite the vast literature on the medical costs of obesity, there is nothing available to answer the question of who pays these costs--the obese themselves, or someone else?