Biliary tract cancers are a consequence of a stepwise malignant transformation of the biliary epithelium. Intrahepatic cholangiocarcinomas arises from any portions of the intrahepatic bile duct epithelium: the segmental or area ducts and their finer branches or intrahepatic small bile ducts. Cholangiocarcinoma arising from the hepatic ducts or near their junction are called hilar cholangiocarcinoma or Klatskin tumour, and are considered as extrahepatic lesion. Cancer of extrahepatic bile ducts may also arise in the Ductus cysticus or choledochus as well as in the gall bladder. For intrahepatic cholangiocarcinoma, the UICC-TNM classification system of malignant liver tumors is applied, differing from the UICC-TNM staging system of extrahepatic bile ducts and gall bladder carcinomas. The cause of carcinomas of the bile ducts remains speculative in most cases. However, chronic inflammation due to sclerosing cholangitis, hepatolithiasis or parasites is associated with carcinogenesis. Histopathologically, the vast majority are adenocarcinomas; mesenchymal tumors and primary melanomas are extremely rare. Different genetic alterations are discussed to be of importance.