This document summarizes adjuvant chemotherapy for breast cancer. It discusses the rationale for adjuvant chemotherapy based on the Fisher hypothesis that breast cancer is a systemic disease at diagnosis. Evidence from large meta-analyses shows that adjuvant chemotherapy improves outcomes compared to no treatment or CMF chemotherapy alone. The addition of anthracyclines or taxanes to chemotherapy regimens provides further benefits. Molecular profiling tools can help select patients who will most benefit from chemotherapy based on tumor biology. Guidelines recommend chemotherapy for higher risk patient subgroups based on tumor characteristics and gene expression profiles.