Roux-en-Y Gastric Bypass is a highly effective bariatric procedure where a small, narrow gastric pouch is formed from your stomach. The pouch is joined to small bowel and then the biliary limb is joined to the alimentary limb further down to divert biliary stream (giving it a Y shape and hence the name). 

It has a long track record of safety and efficacy.  The weight loss outcomes tend to be better than sleeve in long term but it is associated with a higher risk of early and late complications.

It is remarkably effective for those with significant acid reflux but is technically demanding and associated with a higher risk of early and late complications in comparison with sleeve.