About the cover: Cover is based on a computed tomography slice of the lung obtained 2 cm above the dome of the diaphragm at end-expiration in a patient with acute respiratory distress syndrome. The image was digitally adjusted for contrast: red indicates hyperinflated compartments; blue, normally aerated compartments; yellow, poorly aerated compartments; and green, nonaerated compartments. For more information, see article by Terragni and colleagues, beginning on page 160.