Abstract: Non-small cell lung cancer (NSCLC) is the most common type of lung cancer, accounting for more than 80% of all cases. Despite recent advances in the diagnosis and treatment of NSCLC, the prognosis of patients remains poor, with a five-year survival rate of only 15%. Currently, immune checkpoint inhibitors (ICIs) have been approved for lung cancer treatment. Although they exhibit advantages such as high efficacy, durability, and low toxicity, only a small subset of NSCLC patients derives sustained benefits from immunotherapy. With the growing attention to the prognostic role of tumor-infiltrating lymphocytes (TILs) in NSCLC, the search for more effective prognostic biomarkers has become a research priority. This review systematically analyzes the mechanisms, clinical evidence, and evaluation methods of TILs in predicting immunotherapy responses in NSCLC, aiming to provide references for future research and clinical applications.