Obesity is a major epidemic in developed countries. It induces or exacerbates hypertension, diabetes mellitus, obstructive sleep apnea, dyslipidemia, and many other disease processes, which cumulatively contribute to premature mortality on a scale rivaling that of smoking. At present, bariatric surgery is the only therapeutic modality that can produce sustained weight loss and halt or resolve comorbidities. This success results from the ability to perform the operation reliably, usually laparoscopically, with low mortality. The most commonly performed operation is Roux-en-Y gastric bypass. Other bypasses discussed in this review include biliopancreatic diversion with and without duodenal switch. Purely restrictive operations, especially adjustable gastric banding, have a lower risk but are somewhat less effective. We focus on the more controversial aspects of commonly accepted operations, including patient selection, the spectrum and frequency of complications, and the long-term outcome.