Angiotensin-converting enzyme (ACE) inhibitors are a relatively homogenous drug class widely used today. They have been shown to reduce morbidity or mortality in congestive heart failure, myocardial infarction, chronic renal insufficiency, diabetes mellitus, and atherosclerotic cardiovascular disease. Pathologies underlying these conditions are partially attributable to the renin-angiotensin-aldosterone system. Angiotensin II contributes to endothelial dysfunction, altered renal hemodynamics, and vascular and cardiac hypertrophy. ACE inhibitors attenuate these effects. Clinical outcomes of ACE inhibition include lower incidence of fatal and nonfatal myocardial infarction, reinfarction, angina, stroke, end-stage renal disease, and morbidity and mortality associated with heart failure. ACE inhibitors are generally well tolerated and have few contraindications.