The biliary tree consists of intrahepatic and extrahepatic bile ducts and is lined by biliary epithelial cells (or cholangiocytes). There are also peribiliary glands around the intrahepatic large bile ducts and extrahepatic bile ducts. The biliary tree is a conduit of bile secreted by hepatocytes and biliary epithelial cells and also of the peribiliary glands and has several physiological roles. A number of diseases affect mainly the intrahepatic and extrahepatic biliary tree, and, in this special issue, these cholangiopathies are reviewed in detail with respect to genetics, pathogenesis, and pathology. In this paper, the anatomy and physiology of the biliary tree, basic injuries to biliary epithelial cells from stress and bile duct damage, and representative cholangiopathies are briefly reviewed.