A resurgence of interest in clinical auscultation is in progress. Recent technical advances permit more objective observations than were previously possible. Quantified lung sounds are being correlated with clinical, physiologic, and roentgenologic information. The purpose of this article is to summarize current knowledge on the production, transmission, and clinical significance of lung sounds. The complex sonic signals arising in the lung during respiration reflect its mechanical state. More precise understanding of pulmonary sounds and their clinical correlations could lead to powerful diagnostic tools, which have particular appeal because of their noninvasive nature.