Coronary plaque disruption and subsequent thrombosis is the major recognized pathogenetic component of “vulnerable plaques,” which cha- racterize the transition from stable coronary artery disease to acute coronary syndromes. Autopsy studies have characterized a subgroup of high-risk, or vulnerable, plaques that result in acute coronary syndromes or sudden cardiac death. In recent years, cardiovascular research has sought potential strategies for detecting high-risk plaques before their disruption. This review focuses on definition of vulnerable plaque and vulnerable patients and the diagnostic modalities using identification of the vulnerable/high-risk plaques.