This article provides an overview of giant cell tumor, including the typical clinical, radiographic, and pathologic findings, as well as some unusual features, such as multifocality and metastases. The article addresses recent advances in the molecular biology of giant cell tumor, particularly receptor activator of nuclear factor kappa B (RANK)-ligand signaling, in addition to novel anti–RANK-ligand therapy, the use of which seems promising for unresectable and metastatic tumors.