The incorporation of genetic information into clinical oncology practice is a process in evolution, necessitating consideration of cancer risk assessment, ethical and social implications of testing and efficacy of treatment, and prevention interventions. Although most cancers do have a hereditary component, recognizing individuals who are at unusually high risk is important for planning their surveillance practices and considering options for risk management over a lifetime, and because of implications for their family members. Genetic information has enormous potential to inform and transform cancer risk identification, risk reduction, and treatment practices. In this review, we summarize basic information about breast cancer genetics, examine accumulating data about the prevalence and penetrance of deleterious mutations and management options for BRCA1 and BRCA2 mutation carriers, and discuss some of the counseling issues that may occur as physicians and patients explore this exploding area of oncology. The rapid incorporation of careful genetic testing into oncology practice is an important step toward more precise risk management. Currently, the time necessary for careful discussion of the complex issues raised by genetic testing for inherited breast/ovarian cancer susceptibility may necessitate referral to geneticists or genetic counselors for truly informed consent to be obtained. However, identification of women for whom testing is appropriate and management of cancer risk with women after testing, are critical new functions for oncologists. They are only the beginning of exciting new opportunities in cancer risk and prevention.