Chemoprevention in breast cancer represents one of the most important therapeutic regimens in an effort to optimize survival and prevent breast cancer recurrence. The chapter aims to analyze below all potential medical regimens used in breast cancer chemoprevention, along with explaining the reasons why those are the ones selected: their characteristics, their mechanism of action, and their side effects. Among these, we may report tamoxifen, raloxifen, aromatase inhibitors, and new therapeutic regimens such as polyphenoles.