Optical coherence tomography (OCT) is an innovative catheter-based imaging technology that uses light and fiberoptic to obtain unique details of the coronary arteries and stents on a microscope scale. OCT is an efficient method to rapidly map the extension and type of coronary artery disease with the potential to guide complex percutaneous coronary interventions (PCI). It can reliably detect and quantify atherosclerotic plaque characteristics, differentiate early from late stage of atherosclerotic disease and distinguish atherosclerotic (plaque rupture, erosion, calcified nodule) versus non atherosclerotic causes (spontaneous coronary dissection, intramural hematoma) of acute coronary syndromes. Further, it is very sensitive and accurate in detecting calcium and measuring the most relevant parameters (thickness, proximity to the lumen, circumferential extension) that may impact stent expansion. Based on automatic lumen measures and angiographic co-registration, OCT is used to plan and map the procedural strategy of stent implantation in complex lesion cohorts, with identification of the imaging features that require corrective actions to optimize stent results. OCT is a cardinal tool in patients presenting with stent failure (restenosis and thrombosis) to differentiate mechanical from biological causes with the potential of tailored treatment of the root mechanisms.