Progression of atheromatous plaque within neointima of coronary stents, which was termed neoatherosclerosis, has gained interest as a potential cause of very late stent failure. Pathologically, neoatherosclerosis was defined as the development of foamy macrophage clusters, fibroatheroma, thin-cap fibroatheroma, plaque rupture, and in-stent calcification within the stent. Following the pathological observations, a growing number of in vivo studies by using optical coherence tomography (OCT) and coronary angioscopy have been published to date. Those studies tried to clarify the features of neoatherosclerosis and have improved our knowledge substantially. Nevertheless, there still are missing information on natural history and clinical implications of neoatherosclerosis. The present review article summarized the definitions of neoatherosclerosis from the stands of view of pathology, OCT, and angioscopy. Moreover, what is known and what is not known regarding neoatherosclerosis were outlined for better understanding of pathophysiological consequences of coronary stents, which hopefully generates further ideas of clinical investigations.