Recent years have brought great advances in the understanding of the pathogenesis of colorectal cancers. The elucidation of the underlying genetic alterations that produce these cancers has made it possible to broadly categorize this disease into two major types, hereditary and sporadic. The hereditary cancers have been divided further into recognized syndromes, mainly familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer. These syndromes have unique clinical pictures and different prognoses in addition to their different genetic bases. Sporadic cancers have been found to have analogous genetic alterations which propel them along the progression from normal tissue to benign adenoma/dysplasia to malignancy. These advances in genetics can potentially lead to clinically useful advances in detection, treatment, and, ultimately, prevention of colorectal cancer.