Intraductal papillary neoplasm of the bile duct (IPNB) is a grossly visible, preinvasive neoplasm of the bile duct that characteristically shows an intraductal predominant growth in dilated bile duct(s). IPNB is composed of a well-differentiated papillary or villous neoplasm covering delicate and ramifying fibrovascular stalks. Tubular components are usually admixed, although they usually constitute less than 50% of the neoplasm. IPNB is regarded as the counterpart of pancreatic intraductal papillary mucinous neoplasm (IPMN). As in IPMN, IPNB is divided into the intestinal, gastric, pancreatobiliary, and oncocytic subtypes and further classified into low-intermediate-grade and high-grade intraepithelial neoplasms. The cases of IPNB with invasion are called “IPNB with an associated invasive carcinoma.” IPNBs arising in the intrahepatic bile duct and right or left hepatic bile ducts are quite similar to IPMNs, whereas those arising in the extrahepatic bile duct, particularly in the distal bile ducts, show more aggressive features and more tubular components in comparison to IPMNs. Ordinary cholangiocarcinoma with an inconspicuous or low-height intraluminal papillary component, mucinous cystic neoplasms (MCNs), biliary intraepithelial neoplasia (BilIN), and intraductal tubulopapillary neoplasm should be distinguished from IPNB. Molecular and genetic analyses of more cases of IPNB with reference to IPMN are promising for the evaluation of pathologic and biologic heterogeneities associated with IPNB.