β-Adrenergic blockade represents a major pharmacologic advance. These drugs bind to membrane adrenergic receptors interfering with the effects of endogenous catechol-amines. Eight β-blockers are available in the United States, and others are being studied. The drugs have varying pharmacodynamic properties that may modify certain side effects: β1- selectivity, partial agonism, alpha-adrenergic blocking activity, membrane stabilization, and varying pharmacokinetic characteristics. The drugs have been shown to be relatively safe and useful for a wide variety of cardiovascular and noncardiovascular disease states, and their wide spectrum of therapeutic activity illustrates the importance of the sympathetic nervous system in the pathophysiology of medical illness.