Lynch syndrome is the most common hereditary colorectal cancer syndrome, responsible for 3-5% of all colorectal cancer (CRC) cases. In addition, tumors of the endometrium, ovaries, stomach, small bowel, biliary tract, urinary tract, skin and brain occur at higher frequencies compared to the general population. Mutations in at least four different mismatch repair (MMR) genes, including MLH1, MSH2, MSH6 and PMS2, are the underlying defect in Lynch syndrome. The introduction in chapter 2 gives a general overview of different aspects of Lynch syndrome. Clinical features, cancer risks, diagnostic strategies, surveillance and management of Lynch syndrome are discussed. The identification of Lynch syndrome is still suboptimal, mainly due to the lack of specific diagnostic features. Early identification of Lynch syndrome is important for optimal surveillance.