Immune checkpoint inhibitors against programmed cell death-1 (PD-1) or programmed cell death-ligand 1 (PD-L1) are a standard pharmacologic therapy for patients with non–small-cell lung cancer (NSCLC). Substantial data have accumulated in recent years showing that radiotherapy combined with immunotherapy is more effective than monotherapy alone. Preclinical studies have shown that PD-L1 expression is upregulated on tumor cells after radiotherapy, resulting in the synergistically enhanced antitumor effect of irradiation and PD-L1 blockade. In the clinical setting, patients receiving radiotherapy before anti-PD-1 treatment have had a significantly better prognosis than those who have not undergone radiotherapy. In the present report, we reviewed previous studies of the combination of radiotherapy and anti-PD-1/PD-L1 treatment for NSCLC. In addition, we report our case of a patient whose PD-L1 expression gradually increased in brain metastases from NSCLC after repeated radiotherapy. In the perspectives portion, we focused on the questions of how to integrate radiotherapy into anti-PD-1/PD-L1 agent regimens and described several ongoing clinical trials.