Unstable angina, non–Q wave, and Q wave myocardial infarction (MI) comprise the acute coronary syndromes that result from a complex interplay between atherosclerotic plaque rupture and intracoronary thrombosis. A better understanding of the cascade of events leading to the acute coronary syndromes together with prevention and patient education have altered treatment modalities. In particular, attempts to stabilize the atherosclerotic plaque, prevent its rupture, and treat the effects postrupture have greatly reduced mortality. Despite this, the acute coronary syndromes remain a large element of health care resource allocation. This article reviews the progression of the atherosclerotic plaque and the clinical sequelae of plaque disruption, focusing on critical events that result in intracoronary thrombosis.