The American Cancer Society estimated that in 2012 there were 40,290 new cases of rectal cancer in the United States. In the 1980's the standard of care was surgical resection alone, unfortunately this was associated with high rates of local recurrence (30%) in node positive or T3-4 disease. Randomized studies demonstrated the efficacy of adding post-operative and subsequently pre-operative chemo-radiation. Preoperative radiation, either on its own or with concomitant chemotherapy, decreases local recurrence, increases disease-free and overall survival and improves rates of sphincter preservation.