The bile duct system is a pathway of bile transportation from the liver to the intestine and plays a role of exocrine function of the liver. It consists of two different types of epithelial cells, hepatocytes and cholangiocytes. Anatomically as well as developmentally, the bile duct could be divided into intrahepatic bile duct (IHBD) and extrahepatic bile duct (EHBD; extrahepatic hepatic duct, gallbladder, cystic duct, and common bile duct) system. Initially, the secreted bile is transported through the apical side of hepatocytes called as bile canaliculus and then transferred to the duct system (IHBD and EHBD). EHBD characteristically develops the peribiliary glands (PBGs) which are suggested to be a niche of progenitor cell for the hepatobiliary system. Recent studies have revealed that development of IHBD and EHBD is differently regulated during developmental stage of the liver. EHBD arises from a part of the pancreatobiliary domain of foregut endodermal epithelium. In contrast, IHBD develops from the hepatoblasts inhabiting in the fetal liver as a common progenitor cell for hepatocytes and cholangiocytes. In this chapter, we frst show histology of the bile duct system and review recent advances in the regulatory mechanisms of both IHBD and EHBD development.