Achieving clinical and biochemical targets in type 2 diabetes mellitus (diabetes) is fundamental to preventing diabetic microvascular and macrovascular complications. These clinical imperatives are made more challenging in the setting of obesity. This review examines the evidence for bariatric surgery as a means of optimizing diabetes care, addressing diabetes resolution, glucose and lipid metabolism and cardiac effects. Mechanistic evidence of diabetes amelioration is summarized. The question of when bariatric surgery should be offered in the course of obesity-associated diabetes is discussed. Current guidelines and specialist society recommendations for bariatric surgery in diabetes are summarized.