Optical coherence tomography (OCT) is an intravascular imaging modality that enables high-resolution cross-sectional imaging of coronary arteries in vivo. With resolution that is a 10-fold improvement compared with intravascular ultrasonography, OCT can facilitate detailed plaque characterization. This article introduces the basic principles of OCT image acquisition and interpretation. Qualitative analysis entails the evaluation of plaque morphology, including features associated with plaque vulnerability to rupture. Quantitative analysis and recognition of OCT image artifacts are also discussed.