Axillary nodal status is an important prognostic factor in guiding locoregional and systemic treatment for breast cancer. Sentinel lymph node biopsy (SNB) has revolutionized axillary staging by replacing axillary lymph node dissection (ALND) in node-negative women. Even in select patients whose sentinel lymph nodes (SLNs) contain metastases, SNB alone has become an accepted method of managing the axilla. Identification of micrometastases through immunohistochemical analysis of SLNs that are tumor-free on hematoxylin and eosin staining (H&E) does not confer additional clinical benefit. The use of SNB after neoadjuvant chemotherapy (NAC) remains controversial. In addition to axillary nodal status, tumor biology plays an increasingly important role in guiding therapeutic decisions.