The diaphragm performs most of the physiologic work of inspiration, and forms an anatomic barrier between the thoracic and abdominal cavities. Disorders of the diaphragm can be related to impairment of either of these functions, and most have radiologic manifestations. Both intrathoracic and intra-abdominal disease processes can alter the normal radiologic appearance of the diaphragm. Abnormalities are usually first detected on chest radiographs, often incidentally in asymptomatic patients, and many require further characterization by other imaging studies for definitive diagnosis. Fluoroscopy, CT, and MR imaging are frequently the most useful additional studies, whereas ultrasonography, barium contrast studies, and liver-spleen scintigraphy are occasionally helpful. Selection of the most appropriate radiologic technique in a given clinical situation can greatly facilitate the diagnosis of diaphragm abnormalities.