It has been evident for some time that individuals from some families exhibit a genetic predisposition to breast cancer. Since the discovery of the first breast cancer susceptibility gene, BRCA1 in the 1990s, much work has been carried out to identify further breast cancer susceptibility genes. This has led to the identification of another high-penetrance gene, BRCA2, a number of moderate-penetrance genes and, more recently, common low-penetrance genes and loci. The clinical benefit of the identification of such susceptibility genes and loci is in allowing an estimate of the risk of developing breast cancer in carriers. Ultimately, it is hoped that knowledge of an individual's genetic profile in relation to these genes may allow the use of targeted therapies to maximize efficacy in the treatment of breast cancer.