Obesity is associated with a variety of weight-related metabolic comorbidities. Bariatric surgery (metabolic/gastrointestinal surgery) not only achieves significant and sustainable weight loss, but also induces extraordinary effects on nearly all obesity-related comorbidities, particularly remission of type 2 diabetes mellitus (T2DM). The mechanisms underlying such effects are slowly being elucidated, and it appears that the metabolic benefits of bariatric surgery are not only attributable to weight loss, but there are also weight independent mechanisms at play. This article outlines the metabolic effects of the most commonly performed bariatric procedures, with a particular emphasis on how they affect glucose metabolism and T2DM.