• breast cancer;
  • primary prevention;
  • chemoprevention;
  • epidemiology;
  • timing

Despite recent calls to intensify the search for new risk factors for breast cancer, acting on information that we already have could prevent thousands of cases each year. This article reviews breast cancer primary prevention strategies that are applicable to all women, discusses the underutilization of chemoprevention in high-risk women, highlights the additional advances that could be made by including young women in prevention efforts, and comments on how the molecular heterogeneity of breast cancer affects prevention research and strategies. CA Cancer J Clin 2014;64:186–194. © 2014 American Cancer Society.