The use of radical surgery has maximized local control, sphincter preservation, and overall survival in patients with rectal cancer. Despite the advances in surgical techniques, local recurrence still remains a problem. Following potentially curative surgery, the incidence of local recurrence in patients with stages B2, C disease varies from 15% to 65%. There are four major approaches in which radiation therapy (RT) has been used in the adjuvant treatment of rectal cancer. These include postoperative RT +/- chemotherapy, preoperative RT +/- chemotherapy, both pre- and postoperative RT (sandwich technique), and intraoperative RT in conjunction with preoperative external beam RT. In patients with resectable rectal cancer, adjuvant RT has been shown to decrease the incidence of local recurrence and, in some series, may influence survival rates. In patients with locally advanced, unresectable, or recurrent rectal cancer, the use of preoperative radiation therapy, attempted surgical resection, and intraoperative RT further enhances local control.