In the present article, an extensive review of the current knowledge regarding predictive molecular markers in breast cancer is presented. The main emphasis has been given to the adjuvant therapy setting, because of the lack of well-designed studies evaluating predictive markers in the metastatic setting. In the first part of the article some general concepts have been summarized, mainly to emphasize the difference between prognostic and predictive markers. In the second part of the article, studies evaluating molecular markers with predictive value for the most commonly used drugs or regimens (i.e., cyclophosphamide, methotrexate, 5-fluorouracil [CMF], anthracyclines, taxanes, and herceptin) have been reviewed and discussed. An attempt has been made to provide for each single predictive marker the currently available level of evidence, to allow the reader to have immediate information regarding the impact of the evaluated marker in daily clinical practice. In the last part of the article, the most important findings have been summarized and future avenues of research have been outlined.