Bariatric surgery produces substantial, long-term weight loss with reduced morbidity and mortality. Genetics can strongly influence this response, as well as the initial propensity to obesity. Several genes have been implicated but more in-depth mechanistic studies are needed to understand how genes affect energy regulation and mediate the beneficial effects of bariatric surgery. The Obesity Research Biobank Syndicate (ORBiS) aims to fulfil this need. It provides a comprehensive collection of high-quality biological samples and patient data to facilitate mechanistic research and help translate it to improved treatments for patients. Patients undergoing bariatric surgery are recruited from multiple centres in the UK. With informed consent, blood or saliva samples are collected pre-operatively and tissue collected during surgery. Samples include: adipose tissue (subcutaneous and visceral), muscle, liver, stomach and small intestine. Relevant clinical and demographic data are linked and stored pseudo anonymised in a secure database. Tissue collections are transported to and processed in the ORBiS laboratory at University College London, and stored at UCL-Royal Free Hospital Biobank for future use. Research programmes will be supported within and beyond the contributing sites. External researchers will be required to obtain individual REC approval prior to submitting an application.