The number of bariatric surgical procedures performed in the United States has increased steadily during the past decade. Currently accepted criteria for consideration of bariatric surgery include a body mass index (calculated as weight in kilograms divided by the square of height in meters) of 40 kg/m2 or greater (or >35 kg/m2 with obesity-related comorbidities), documented or high probability of failure of nonsurgical weight loss treatments, and assurance that the patient is well informed, motivated, and compliant. Appropriate patient selection is important in achieving optimal outcomes after bariatric surgery. In this article, we review our approach to the medical and psychological assessment of patients who want to undergo bariatric surgery. The medical evaluation is designed to identify and optimally treat medical comorbidities that may affect perioperative risks and long-term outcomes. The psychiatric and psychological assessment identifies factors that may influence long-term success in maintaining weight loss and prepares the patient for the lifestyle changes needed both before and after surgery.