Coronary thrombosis is the most common cause of acute coronary syndromes (ACS), including sudden cardiac death. Plaque rupture in most cases, plaque erosion uncommonly, and calcified nodule rarely have been demonstrated to be the main mechanisms underlying acute coronary thrombosis in both ex vivo and in vivo studies. In the setting of ACS, high-resolution intravascular imaging with OCT can characterize plaque pathology at the time of intervention in order to better understand the etiology of ACS and develop personalized treatment strategies leading to improved long-term outcomes. Spontaneous coronary artery dissection (SCAD) is another rare but important cause of ACS with an incidence of 0.1 to 2.1%. While diagnostic accuracy of angiography for SCAD is limited, OCT can provide substantial insights into the morphologic features of the condition. Finally, OCT allows detailed in vivo examination of the morphologic characteristics of coronary arteries in patients with coronary spasm (CS), which plays an important role in the pathogenesis of an acute coronary event.