Colorectal cancer (CRC) accounts for over 8% of all deaths annually worldwide. Between 2 and 5% of all CRCs occur due to inherited syndromes, including Lynch syndrome, familial adenomatous polyposis, MUTYH-associated polyposis, Peutz-Jeghers syndrome, juvenile polyposis and Cowden/PTEN hamartoma syndrome. In addition, serrated polyposis is a clinically defined condition characterised by multiple colorectal serrated polyps and an increased risk of CRC but the genetics are not known. In most hereditary CRC syndromes, polyps undergo carcinogenesis, but the exact route to carcinoma seems to differ between the conditions. Discovery of the key germline mutations in these syndromes has been instrumental to our understanding of the underlying molecular mechanisms of colorectal carcinogenesis. This review summarises the genetic and pathological alterations in hereditary CRC syndromes.