Adenocarcinoma of the colon and rectum is one of the most common human malignancies. It is a major public health issue in developing and underdeveloped countries. In developed countries, thanks to screening, removal of neoplastic polyps, and advances in surgery, radiation, and chemotherapy, there has been a small but persistent improvement in survival over the past two decades, improvements that have not yet been seen in the rest of the world. This chapter reviews progress in understanding the biology of colon cancer, the epidemiology and prevention of colon cancer, and its diagnosis and treatment.