Colorectal cancer is a common disease that frequently produces limited survival in afflicted patients. Recently a genetic model for tumorigenesis has been defined and has led to a better understanding of the interrelationships between environmental mutagens and genes. Epidemiologic studies have identified multiple chemopreventive agents that appear to reduce the risk of developing colorectal cancer. Their molecular mechanisms of action, as related to the genetic model for colorectal cancer, are discussed.