Strategies for preventing colorectal cancer will be more effective if they are based upon a thorough understanding of the evolutionary pathway leading from normality through to malignancy. Fundamental insights into the process of colorectal carcinogenesis have been achieved through the advent of molecular technologies. DNA technology also offers the promise of powerful and highly specific tests for detection of cancer and precancerous lesions (Smith-Ravin et al 1995). This chapter will review the major molecular breakthroughs of the last decade, integrating genetic changes with their morphologic counterparts.