Bone-forming tumors represent a broad spectrum of neoplasms that arise within or on the surface of bone and may rarely occur in extraskeletal sites. The hallmark of these tumors is that the neoplastic cells produce the organic components of bone or bone matrix that may or may not be mineralized. Osteoma is usually solitary but in rare cases may be multiple. The latter is seen typically in association with Gardner syndrome. Osteoid osteoma and osteoblastoma are terms used to describe benign bone-forming tumors with essentially identical histologic features, thus preventing their distinction from one another solely on histomorphologic grounds. They differ in size, anatomic sites, and clinical manifestations. Osteosarcoma is the most common primary malignant tumor of bone, exclusive of hematologic malignancies. Although the tumor may occur at any age with a slightly male predilection, it has a bimodal age distribution, with a propensity to develop predominantly in adolescents and young adults. This is followed by a smaller second peak in the elderly, frequently with conditions known to predispose to osteosarcoma, including Paget disease and prior radiation.