Adenocarcinomas of the intra- and extrahepatic bile ducts are rare tumors that begin with malignant transformation of the bile duct epithelia. Intrahepatic cholangiocarcinomas derive from the small bile ducts located proximally to the right and left hepatic ducts. Extrahepatic bile duct carcinomas originate in the right or left hepatic duct, the cystic duct, or the choledochal duct. Tumors located at the bifurcation are called Klatskin tumors. The intrahepatic cholangiocarcinomas are classified according to the TNM classification of liver tumors, while the extrahepatic bile duct tumors have their own TNM classification. Several factors, accompanied by a chronic inflammatory reaction, have been discussed in the etiopathogenesis of these tumors: schistosomiasis, ulcerative colitis with primary sclerosing cholangitis, and inborn bile duct cysts of the liver as a consequence of a disturbance of the ductal plate formation. Over 95% of bile duct tumors are adenocarcinomas. In the nomenclature of precursor lesions a two-grade classification of dysplasia (low-grade versus high-grade) has been found to be more reproducible.