By identifying individuals with an increased risk of breast cancer, health professionals can offer prevention strategies tailored to individual risk levels. Such strategies may include early initiation of cancer screening, more frequent screening, targeted therapeutic or behavioral interventions, or prophylactic surgery. In order to achieve clinical benefits with this approach, however, risk assessment strategies and effective prevention measures must be available. In this article we review current knowledge about cancer risk assessment for unaffected women and probability models for identifying individuals who are carriers of a mutation in BRCA1 or BRCA2, the two genes most commonly implicated in hereditary breast cancer. We review BRCA1 and BRCA2 mutations in various ethnic populations and how this information factors into risk assessment. Additionally, we summarize the current guidelines for when to make a referral to genetic services for risk assessment and evaluation.