Lung cancer remains the leading cause of cancer-related mortality worldwide. Many patients have lost the chance of surgery when diagnosed. The prognosis of advanced non-small cell lung cancer (NSCLC) is poor, and radiotherapy (RT) and chemotherapy are the main treatment. With the application of immune checkpoint inhibitors (ICIs), the survival of patients has been greatly improved. However, the response rate of immune checkpoint inhibitors alone remains suboptimal, and the efficacy of immunotherapy can be improved when combined with radiotherapy, especially the addition of low-dose radiotherapy, which can not only control local lesions but also enhance the systemic anti-tumor effect. At present, there are still controversies about the timing of radiotherapy combined with immunotherapy, predictive indicators of efficacy, and the selection of fractionation, dose, and site of radiotherapy. This chapter reviews the progress of radiotherapy combined with immunotherapy for locally advanced and advanced NSCLC, providing evidence-based recommendations to guide clinical practice.