Following radical cystectomy, muscle-invasive bladder cancer remains associated with a substantial risk of locoregional recurrence, particularly in patients with pT3–4 disease, nodal involvement, positive surgical margins, or limited pelvic lymph node dissection. Historically, adjuvant radiotherapy reduced pelvic recurrence rates but was largely abandoned because of toxicity concerns associated with older radiation techniques. The development of intensity-modulated radiotherapy, image-guided radiotherapy, contemporary contouring guidelines, and modern dose constraints has renewed interest in adjuvant radiotherapy. Recent randomized trials, including Bladder-ART/GETUG-AFU30 and BART, have demonstrated that modern adjuvant radiotherapy can be safely delivered and significantly improve locoregional control in selected high-risk patients. Current International Bladder Investigator Society recommendations have standardized target volume delineation, including pelvic nodal regions and cystectomy bed. At the same time, the management of muscle-invasive bladder cancer is rapidly evolving with the integration of immune checkpoint inhibitors, antibody–drug conjugates and circulating tumor DNA-guided based treatment strategies. Future research should focus on refining patient selection and integrating adjuvant radiotherapy within a personalized multimodal approach combining clinicopathological risk factors, molecular biomarkers, and contemporary systemic therapies.