The term vulnerable atherosclerotic plaque is used to describe an atherosclerotic lesion with a high probability of rupture and thrombosis causing an acute coronary event or stroke. Pathogenesis of the vulnerable plaque has been well described pathologically and on experimental models. Detection of vulnerable plaques in vivo has been limited so far. There has been lack of methods able to predict future event from certain lesion characteristics that were rigorously validated on prospective clinical trials. Intravascular near-infrared spectroscopy is a novel technique that has been intentionally developed for the identification of a lipid core within a plaque. Results from recent clinical trials seem promising. This review briefly summarizes current knowledge in the field of near-infrared spectroscopy.