This chapter reviews the factors involved in deciding which operation to perform for an operative candidate. Roux-en-y gastric bypass is the most common weight loss procedure performed in the United States and is a mixed restrictive and malabsorptive procedure. For many patients, government policy may also determine the operative procedure options. Patients are generally better informed and capable of deciding which bariatric operative procedure would be best for them. Past surgical history of a patient can factor into the decision making process. This information can change the surgeon's operative approach, especially if the patient has had prior gastric surgery. Patients with a history of eating high calorie liquids, such as ice cream, must change their eating habits as this is one way to fail any bariatric procedure. Some patients will have personality characteristics that may make them better candidates for one procedure over another.