 Over the last three decades, a steady shift has occurred in the management of breast cancer. Because it was traditionally viewed as a local disease, many advocated the use of radical surgery to achieve maximum survival benefit. This view has been slowly replaced by a broader biologic view that recognizes the often systemic nature of breast cancer, even when it appears to be localized to the breast. Results from randomized clinical trials have demonstrated that less extensive surgery or lumpectomy plus radiation therapy are optimal for local management of early breast cancer. In addition to the less radical approach to surgical treatment of breast cancer, other randomized clinical trials established the value of postoperative adjuvant systemic therapy in improving overall survival by eradicating micrometastatic disease, the major cause of mortality from breast cancer. An improved survival has been shown from using chemotherapy as well as the antiestrogen tamoxifen in the adjuvant setting and has been confirmed through the overview analyses from the Early Breast Cancer Trialist Collaborative Group. Despite the well-documented benefits of adjuvant systemic therapy, it is not effective in preventing death from breast cancer in all patients who are candidates for such treatment. The worth of such therapy can only be judged in retrospect upon disease relapse, a time when breast cancer is nearly always incurable. Currently, there are few reliable methods to predict the success or failure of a particular postoperative treatment modality and better ways to predict and optimize outcome are needed. Preoperative primary, neoadjuvant systemic therapy is an alternative approach that is based on a strong rationale. With the tumor still in place and directly accessible, this form of therapy allows direct observation of response to treatment which may predict the likelihood of controlling distant micrometastatic disease and also enables the sampling of tissue to explore molecular correlates of response and also the mechanisms of action of therapeutic agents. Furthermore, it allows early identification of patients with refractory disease who might benefit from alternative treatments before they develop macrometastatic disease and miss the opportunity for a cure. Primary systemic therapy can also help facilitate surgery and debulking of disease in those patients with initially inoperable tumors, as well as improve the odds of breast conservation. 