The incidence of breast cancer is rising in all industrialized countries. In France, with 41,000 new cases and 11,000 deaths per year, breast cancer is still the first cause of death from cancer in women. Genetic familial breast cancer is rare (only-2% due to mutated BRCA1/2 genes). Most of the increase is due to sporadic cases associated with hormonal, reproductive and nutritional factors, some of which can be avoided. Prevention should include: - avoidance of risk factors such as alcohol, obesity, smoking, sedentarity, and, when possible, late first pregnancies and absence of breast feeding. - Lesser use of hormone replacement therapy, in order to avoid the tumor-promoting action of ovarian hormones; this is supported by the strong fall in the incidence of breast cancer in U.S.A after 2002, following a drop in the use of HRT by post-menopausal women. - For very-high-risk women (BRCA 1/2 mutations, or in situ carcinoma with proliferative atypia), chemoprevention with SERM should be authorized, based on randomized trials of tamoxifen and raloxifen. New trials of other agents should be encouraged. - Risk indexes such as that developed by the NCI should be more widely used. - More research on the early steps of human mammary carcinogenesis should be encouraged, as this should lead to individual targeted prevention.