Persons with obesity are more likely to suffer from many other serious health conditions and are more likely to die young. Lifestyle interventions have not been found to be an effective long-term solution for treating obesity. When usual weight loss measures are not successful, bariatric, or 'weight loss,' surgery may be considered. Bariatric surgery is performed to help people with obesity achieve weight loss which they can maintain. Weight loss following bariatric surgery leads to improvement in health and well-being, and patients have been shown to live longer. It is invasive surgery which has surgical risks and potential side effects, including death. Since people are having this surgery to improve their health, it is important that the surgery is performed with a minimum of side effects, otherwise it cannot be justified. Information is collected about the surgery, any complications after the surgery, weight at various time points, and if the patient has diabetes and how it is is treated. Patient details are needed to be able to identify patients on the registry and track their progress through data linkages. Participants have information about their bariatric surgery provided to the registry by their surgeon or hospital. They may also be contacted directly by the registry staff to see if they had any complications and if the surgery had any effect on their health (if they have diabetes), weight, and well-being. The Registry will hold their identifiable information as it aims to follow each patient for ten years after their first bariatric operation. By systematically collecting information on every procedure performed in Australia and New Zealand, the registry will help to identify when surgeons, hospitals or procedures not performing to the expected standard. A Bariatric Surgery Registry should also be able to demonstrate how effectively bariatric surgery results in weight loss and improved health (using diabetes as a marker of health) across the two countries.