Cough is a complex defensive reflex whose purpose is protection of the respiratory tract. There are many nonrespiratory causes, particularly pulmonary congestion from heart disease. Coughs may be useful, useless, or harmful. Treatment based on etiology and type of cough requires only a few medications whose efficiency has been demonstrated. The meaning of cough as a symptom must be carefully determined before rational treatment can be planned. Recent researches on the physiology of the cough reflex, the bronchi, and the mechanisms of bronchial secretion have made it possible for a physician to plan a treatment program on a firm, scientific basis, rather than on tradition.