Hamartomas are the most common benign pulmonary neoplasm. They are usually solitary asymptomatic peripheral masses discovered incidentally as “coin lesions” on chest x-ray film. They are composed of mature mesenchymal elements, most often mature cartilage, but they can also be composed of adipose tissue, fibrous or fibromyxoid tissue, smooth muscle, and/or bone with or without bone marrow. The typical chondromatous hamartoma may have calcifications that gives rise to a characteristic “popcorn calcification” appearance on chest x-ray film. They have been called mesenchymomas, reflecting the observation that they are neoplasms with genetic mutations and are not true “hamartomas.” Entrapped pulmonary epithelium, often entrapped in cleft-like spaces between lobules of cartilage, may be present. The majority are intraparenchymal, and a small minority (about 10%) are endobronchial. Grossly, hamartomas generally range from 1 to 3 cm and are very sharply demarcated so that they can often be “shelled” out by the surgeon. The color and texture depend on the histologic composition. As expected, because most are chondromatous, the majority have a cartilaginous appearance and texture on gross examination. Endobronchial hamartomas are polypoid and are typically composed of adipose tissue as the majority constituent.