The identification of susceptibility genes for specific types of cancer provided the necessary information for the complete characterization of inherited cancer syndromes. The close observation of carrier families has significantly enriched our knowledge on distinct phenotypical features, age of onset and survival rates for each syndrome and gave the opportunity to further understand the molecular basis of hereditary cancer. Recent advances in cancer genetics involve the identification of novel genes with moderate risk to cause cancer, after synergism with particular environmental factors, and therefore reinforcing the genetic component in relation to cancer predisposition. The available genetic tests can constitute an essential step of primary health care, as they can dramatically affect the quality of a cancer patient's life and they can also offer prompt diagnosis for the patient's close relatives. This review reports the most characteristic hereditary cancer syndromes along with their phenotypical and genetic variables that have been described, but it mainly focuses on Hereditary Non-Polyposis Colorectal Cancer (HNPCC), which is linked to pathogenic mutations in one of the mismatch repair (MMR) genes MLH1, MSH2, MSH6, Familial Adenomatous Polyposis (FAP) caused by high-penetrant mutations within the APC gene and Hereditary Breast/Ovarian Cancer (HBOC) linked to mutations within BRCA1 and BRCA2 genes.