Chest wall masses are relatively uncommon in clinical practice. The chest wall contains a number of distinct tissues, including skin, fat, muscle, bone, cartilage, lymphatics, blood vessels, and fascia. Each of these component tissues has the capability of producing either a benign or a malignant primary chest wall mass. Initial clinical evaluation includes careful history-taking; CT scans; MRI; and fine-needle aspiration as the former cannot always distinguish between malignant and benign masses. The benign primary masses of the chest wall are described and include infectious masses such as sternal infections; sternoclavicular joint infections; and osteomyelitis of the rib. Benign neoplasms of the chest wall are listed and include bone and cartilage neoplasms such as osteochondromas and chondromas. Malignant primary masses of the chest wall are listed and include soft tissue sarcomas; plasmacytoma; chondrosarcoma; and synovial sarcomas. Secondary chest wall masses are also defined as direct extensions of a malignancy from a contiguous organ. Breast and lung cancer are the most common. The initial evaluation centers on staging the underlying disease. Figures show a sternoclavicular joint infection; a CT scan showing sternoclavicular joint infection; and a chest wall sarcoma. Tables describe the classification of primary and secondary chest wall masses; benign neoplasm of the chest wall by site of origin; and primary malignant chest wall masses according to tissue of origin. This chapter contains 11 figures, 3 tables, 57 references, 5 Board-styled MCQs, and 1 Teaching Slide Set.