Combined modality therapy is an integral component in the management of rectal cancer. There are two components of adjuvant therapy: pelvic radiation and 5-FU based chemotherapy. In patients with clinically resectable disease, the role of radiation therapy is to decrease local recurrence and increase the chance of sphincter preservation. In patients with locally advanced/ unresectable disease, radiation therapy has the added role of increasing the resectablility rate. The role of chemotherapy, regardless of the resectability status, is to enhance the benefits of radiation (radiosensitization) as well as improve survival by decreasing the incidence of distant metastasis. This chapter will examine the rationale and results of preoperative and postoperative therapy in patients with clinically resectable rectal cancer treated in the adjuvant setting. The results of radiation therapy will be presented followed by a discussion of combined modality therapy.