The intrahepatic biliary epithelial cells or cholangiocytes are the primary focus of injury in many congenital and acquired liver diseases of childhood. Although cholangiocytes account for only 3 to 5% of the liver cell population, injury and progressive loss of intrahepatic bile ducts can result in considerable morbidity and mortality. Table 1 provides an overview of the various disorders that affect the intrahepatic biliary tree. The more common disorders are discussed in detail below. One of the most important cholangiopathies, biliary atresia, characterized by complete destruction of the extrahepatic biliary tree, with variable involvement of the intrahepatic bile ducts, is discussed elsewhere in this series of articles. There has been considerable progress in our understanding of the embryology and physiology of the intrahepatic biliary system. These topics are also selectively reviewed, with an emphasis on advances that aid in the understanding of the pathophysiology of the disorders which affect the biliary tract in children.