Inherited MMR deficiency, i.e. Lynch syndrome, gives rise to a broad spectrum of tumors, especially colorectal and endometrial cancers, but also ovarian, gastric, urinary, small bowel, brain and bile duct/gallbladder cancers. The history of international Lynch syndrome research can be traced back to 1895 and the discovery of a family cancer syndrome. The disease was characterized by Henry T. Lynch in 1966 and came to be known as Hereditary NonPolyposis Colorectal Cancer (HNPCC), which in honour of Dr. Lynch’s findings, was later termed Lynch syndrome. The molecular genetics era began in 1993 when a germline MMR gene mutation was identified as a cause of LS. Currently Lynch syndrome research is being actively carried out worldwide, with an approach that focuses on obtaining a deeper understanding of the molecular mechanism behind LS, enabling preventive diagnosis and personalized medical care.