High density material, including calcium and a variety of other substances, can be seen in the lungs in the setting of many iatrogenic, metabolic, infectious, neoplastic, occupational, and idiopathic disorders. The high density substance in the lungs typically is inconsequential, but it can be an important diagnostic clue to the cause of underlying pulmonary disease. High density material in the lungs can be confusing to radiologists, either due to similar appearances of imaging patterns or to the rare occurrence of some responsible entities. Chest CT is suited uniquely to characterize these patterns, with its high intrinsic contrast of dense material against the lung parenchyma. This review examines chest radiographic and chest CT patterns of high density material in the lungs and provides an approach to the differential diagnosis to familiarize radiologists with these disorders and improve diagnostic accuracy.