Purpose of Review <p> This chapter summarizes the role of optical coherence tomography (OCT) in guiding percutaneous coronary intervention (PCI), highlighting its impact on lesion assessment, optimal stent sizing and placement, and post-procedural optimization.</p> Recent Findings <p> OCT has shown to improve procedural and long-term clinical outcomes over angiography alone. It offers high-resolution imaging that enables precise plaque characterization, including fibrous, lipid-rich, and calcific morphologies, with direct implications for lesion preparation. Accurate measurement of vessel size and lesion length enables stent selection and landing zone identification. After stent deployment, OCT identifies suboptimal results such as underexpansion, malapposition, edge dissections, and tissue prolapse, guiding immediate optimization. The use of OCT is now endorsed with a Class Ia recommendation by European and U.S. guidelines.</p> Summary <p> By enabling anatomy-based procedural planning and results assessment, OCT has transformed PCI into a more precise procedure. Its use contributes to reduced complications, improved stent placement, and better long-term outcomes.</p>