It has been nine years since intravascular ultrasound imaging(IVUS) was for the first time performed in Japan at our hospital. During this period, the progress of catheter technology brought about many improvements in catheter design and image quality. Also clinical utility of IVUS has been widely recognized with accumulation of clinical experiences. The most important feature of this method is the capability of both quantitative and qualitative analyses of the atheroma. IVUS has mainly been used to help guide procedures during catheter interventions and has provided information about the mechanisms of dilatation and restenosis. Recently, the ability of IVUS in diagnosing morphologic changes such as compensatory enlargement, vessel shrinkage and plaque rupture has much attention. IVUS should enhance our understanding of the pathophysiology of coronary artery disease.