Colorectal cancer (CRC) is one of the most common neoplasia in Western countries and the second leading cause of cancer-related death. The vast majority of cases belong to sporadic forms, whereas a small but relevant proportion of them corresponds to inherited disorders, i.e. familial adenomatous polyposis and Lynch syndrome. These individuals with germline mutations in cancer-promoting genes, along with those who had already developed a colorectal neoplasm, either adenoma or carcinoma, stand to benefit from chemopreventive interventions. A large body of evidence indicates that the use of aspirin and other non-steroidal anti-inflammatory drugs (NSAID) can reduce the risk of CRC. Experimental studies have demonstrated that these drugs decrease the incidence of carcinogen-induced colon tumors in rodents, and several epidemiological investigations and therapeutic trials have also shown a 40-50% reduction in the risk of colorectal adenoma and cancer in individuals taking NSAIDs. Moreover, patients with familial adenomatous polyposis taking sulindac or celecoxib experience a reduction in adenoma size and number. The chemopreventive effects of NSAID are largely related to inhibition of cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase that catalyzes the conversion of arachidonic acid to prostaglandins. COX-2 overexpression is a frequent, but not universal event in colorectal neoplasms. Indeed, approximately 50% of adenomas and 80% of CRC express high levels of COX-2 mRNA and protein in neoplastic tissue. In this article, we will review the role of cyclooxygenase as a target for CRC chemoprevention, with special attention to the use of selective and non-selective COX-2 inhibitors in both individuals genetically predisposed and those who have already developed a colorectal neoplasm.