Our understanding of hereditary forms of breast cancer has made enormous advances over the past 15 years, based on epidemiological and molecular genetic studies, and the development of a vast number of informative genetic markers. These studies have involved women with both familial and sporadic forms of breast cancer. Genetic susceptibility to breast cancer can involve several modes of inheritance: Mendelian inheritance, mostly involving autosomal dominant mutations with high penetrance and a high risk of malignancy (the BRCA1, BRCA2, TP53, PTEN and STK11 genes); dominant mutations associated with a lower risk (ATM, BRIP1, PALB2, etc), and multigenic patterns involving common susceptibility variants, i.e., polymorphisms located within predisposing gene loci (FGFR2, TNRC9, MAP3K1, LSP1, etc.) or intergenic regions. Other predisposing factors remain to be discovered, as genetic factors associated with a high breast cancer risk (BRCA1, BRCA2, TP53, PTEN STK11, etc) are only found in about 20% of genetically screened breast cancer families. So far, only the first class of genes have found clinical applications, guiding the choice of medical or surgical treatment. More refined individual risk profiles will benefit from genome-wide polymorphic DNA variant studies anda better understanding of the impact of non genetic factors, such as the obstetrical and gynaecological history, and mutagen exposure.