Breast cancer ranks as the second most common cause of cancer death among women in the United States. Anticancer agents are an important component of breast cancer therapy. Drugs frequently used to treat breast cancer include methotrexate, 5-fluorouracil (5-FU), cyclophosphamide, anthracyclines, taxanes, trastuzumab, tamoxifen, and aromatase inhibitors. These agents inhibit breast cancer progression by a variety of different mechanisms. This review describes each of these drugs and the varying effects each of them have upon breast cancer cells.