Endocrine therapy is a mainstay for the many women who develop in situ or invasive steroid receptor-positive breast cancer. The use of tamoxifen has reduced mortality in such women. Recently estrogen deprivation strategies have come under scrutiny. Here the use of aromatase inhibitors for treatment of postmenopausal endocrine-responsive breast cancer in the metastatic, adjuvant, and preoperative settings is reviewed.