Summary: This is the protocol for the biliopancreatic diversion procedure in the mouse. This procedure is historically thought to be a malabsorptive procedure and has several variations in the human. In brief, the biliary and pancreatic secretions are physically separated from gastrointestinal chyme flow until a point near the terminal small bowel. In theory this leads to significant malabsorption, though when this procedure is done clinically many times a gastric restriction component is also added.