Pulmonary function testing (PFT) is an important component of the evaluation, monitoring, and management of patients with suspected or established lung disease. Spirometry is easily accomplished in the primary care office setting; determination of lung volumes and diffusion capacity is performed in a pulmonary laboratory. Spirometry evaluates vital capacity of the lungs and expiratory flow rates and provides both numeric data and a graphic depiction of respiratory air flow. Characteristic patterns in spirometry-derived data allow the clinician to identify potential lung disease, as well as establish relative reversibility of airflow abnormalities.