The common bile duct, sometimes abbreviated as CBD, is a duct in the gastrointestinal tract of organisms that have a gallbladder. It is formed by the confluence of the common hepatic duct and cystic duct and terminates by uniting with pancreatic duct, forming the ampulla of Vater. The flow of bile from the ampulla of Vater into the duodenum is under the control of the sphincter of Oddi.

When the sphincter of Oddi is closed, newly synthesized bile from the liver is forced into storage in the gallbladder. When open, the stored and concentrated bile (now mixed with pancreatic secretions) exits into the duodenum and takes part in digestion. This conduction of bile is the main function of the common bile duct. The hormone cholecystokinin, when stimulated by a fatty meal, promotes bile secretion by increased production of hepatic bile, contraction of the gallbladder, and relaxation of the sphincter of Oddi.