Abstract: Catheter-based percutaneous coronary intervention has become a crucial approach for treating obstructive coronary artery disease and is widely applied in clinical practice.Although the new generation of drug-eluting stents (DES) has significantly reduced the incidence of post-procedural restenosis and improved long-term clinical outcomes, in-stent restenosis (ISR) remains one of the key challenges affecting the long-term efficacy of percutaneous coronary intervention.Recent studies have demonstrated that DES still have certain inherent limitations.From the metallic stent platform, drug coating to the polymer carrier, each component may exert varying degrees of biological effects on the vascular intima.Optical coherence tomography (OCT), as a high-resolution intravascular imaging technique, has shown significant value in the mechanism research, etiological diagnosis, and clinical classification of ISR.It can clearly identify the tissue composition and morphological characteristics of ISR, providing a precise basis for the formulation of individualized treatment strategies.This review aimed to systematically search the existing literature, comprehensively review the clinical and pathological features of ISR after DES implantation, focus on the OCT-based ISR classification system, and summarize the current treatment strategies and latest advances for ISR.