Recent advances in intravascular imaging have significantly improved the ability to detect high-risk, or vulnerable, plaque in vivo. Coronary angioscopy is especially suitable for identifying thrombus, plaque disruption, and variations in color of the coronary arterial wall. Intracoronary thrombus and disruption of glistening yellow plaque at the site of culprit lesions are seen more commonly in patients with acute myocardial infarction and unstable angina than in patients with stable angina. Acute coronary syndromes occur more frequently in patients with yellow plaque than in those with white plaques. Angioscopy can also be used to assess the effect of preventive treatment. Lipid-lowering therapies with statin change lesions from yellow to white, suggesting plaque stabilization. Coronary angioscopy provides a great opportunity to understand pathophysiology of acute coronary syndrome and would play an important role to evaluate the risk of the future coronary events.