Biliary tract cancers, including intrahepatic, perihilar, and distal cholangiocarcinomas, as well as gallbladder cancer, are a heterogeneous group of cancers with distinct molecular characteristics in each anatomic and pathological subtype. The pathological classification of BTC includes grossly classifiable growth patterns, such as mass-forming, periductal infiltrating, and intraductal growing. The small duct and large duct types of intrahepatic cholangiocarcinoma have been recently introduced in the WHO classification. Typical clinical presentations and various radiological, endoscopic, and molecular modalities for diagnosis are described in detail. To overcome the limitations of traditional tissue acquisition, new diagnostic modalities are being investigated. In fact, the treatment landscape is evolving rapidly owing to the emergence of distinct subgroups harboring unique molecular alterations with corresponding targeted therapies. In addition, we highlight the key points in the diagnostic process in real-world clinical practice for biliary tract cancer.