Carcinomas of the biliary tract are aggressive malignancies, with 5-year survival of less than 10%. These carcinomas arise throughout the biliary tree and are anatomically classified as either intrahepatic or extrahepatic cholangiocarcinomas. Gallbladder carcinomas also arise from the biliary tree but have distinct natural histories compared to cholangiocarcinomas, suggesting different underlying tumor biology. Cholangiocarcinoma incidence varies widely between geographic regions, reflecting the impact of different underlying etiologies. In endemic areas, liver fluke infections by O. viverrini and Clonorchis sinensis, both group I carcinogens, represent the major risk factor for cholangiocarcinomas. In nonendemic regions, other risk factors, including choledochal cysts (603003), hepatolithiasis, and primary sclerosing cholangitis (613806), are likely contributors (summary by Chan-on et al., 2013). Overall, the majority of patients lack such identifiable risk factors (summary by Jiao et al., 2013).