Structural changes occur in the respiratory system with advancing age. Lung elasticity decreases, stiffness of the chest wall increases, and respiratory muscle strength declines. These alterations contribute to gradual, but progressive, reductions in forced vital capacity, expiratory flow rates, diffusing capacity, gas exchange, ventilatory drive, and respiratory sensation. Cigarette smoking accelerates the age-related decline in flow rates. Understanding the effects of aging on the lung is important in order to distinguish pathologic changes from changes that are part of the normal aging process.