Lynch syndrome (LS) is an autosomal dominant genetic condition caused by mutations in the DNA mismatch repair (MMR) genes in the germline. Colorectal cancer and/or LS-associated cancer are more likely in people who carry pathogenic mutations in these genes. Cancers of the endometrium, small intestine, stomach, pancreas, and biliary tract, ovarian, brain, upper urinary tract, and skin are among the cancer types linked to LS. The criteria for a clinical diagnosis of LS, as well as the processes for genetic testing to identify carriers of pathogenetic mutations in MMR genes, have been known for a long time. The precise description of the pathogenicity associated with MMR genetic variants is critical in the mutation detection analysis, especially in order to enroll mutation carriers in endoscopic surveillance programs that are more suited to them. As a result, this may aid in the improvement of LS-related cancer prevention efforts. In this review, we discuss recent advances in the molecular genetics of LS.