Intravascular Optical Coherence Tomography has been explored as an imaging tool for vessel wall and thrombus characterization. OCT enables a high resolution arterial wall imaging, and light properties allow tissue characterization. It has been proved one of the most valuable imaging modalities for the evaluation of vulnerable plaque and thrombus. OCT has a unique capacity in volumetric quantification of calcium, and unlike ultrasound, light can easily penetrate calcified plaques. Finally, this review paper will address aspects of the validation method of plaque characterization and potential pitfalls and put in perspective new approaches that may help the evolution of the field.