Radiation therapy is an effective treatment for muscle-invasive bladder cancer. It can produce complete eradication of tumor, sustained local control, and prolonged survival for selected patients who would otherwise die of the disease. All patients with muscle-invasive bladder cancer should be evaluated for cystectomy and radiation therapy, and the most appropriate treatment should be selected based on individual patient and tumor characteristics to yield the highest probability of cure, the lowest toxicity, and the highest possible quality of life. Advances in image-guided intensity-modulated radiation therapy and improved understanding of the radiation biology of tumors and normal tissues will further these goals and result in greater proportions of cured patients with intact, functional bladders.