Breast cancer is one of the most common cancers in women. The goal of the primary prevention of breast cancer is to avert the development of cancer in healthy women. Medications such as tamoxifen and raloxifene prevent development of breast cancer by interrupting the process of initiation and promotion of tumor. The antiestrogenic effects of these agents lead to growth inhibition of malignant cells. Screening for breast cancer can lead to the detection of preinvasive lesions such as ductal carcinoma in situ (DCIS) and early small node-negative cancers. Mammography reduces the mortality of breast cancer. Although the incidence of breast cancer increases with age, few studies have investigated the efficacy of mammography in women older than age 70. In women at high risk for breast cancer because of genetic syndromes, MRI of the breast is found to be more sensitive than mammography alone.