Understanding the physiologic effects of changes in posture and position on normal respiratory function can facilitate their therapeutic application in the clinical setting. In healthy subjects, recumbency reduces lung volumes, increases the impedance to ventilation, and alters the regional distributions of ventilation and perfusion. Patients with airflow obstruction may experience orthopnea due to increases in airway resistance and regional gas trapping. Knowledge of the postural changes in pulmonary function and symptoms that occur in certain neuromuscular diseases may suggest a diagnosis (e.g., diaphragmatic paralysis) and allow for appropriate therapeutic intervention. Lateral decubitus positioning with “the good side down” can significantly improve oxygenation in many adult patients with unilateral parenchymal lung disease (e.g., lobar pneumonia). In the intensive care unit, continuous rotational therapy has been reported to reduce pulmonary complications. Because prone positioning can significantly improve pulmonary oxygen exchange, it often proves useful as a therapeutic adjunct to mechanical ventilation in patients with acute respiratory distress syndrome and refractory hypoxemia.