Sentinel lymph node biopsy (SLNB) has revolutionized the surgical management of the axilla for patients with early breast cancer. SLNB initially became standard regional therapy for women who were both clinically and pathologically node-negative. Subsequently, SLNB has been established as appropriate management in patients with very low axillary tumor burden, defined as isolated tumor cells or micrometastatic disease (< 2 mm); it provides accurate staging information with no detriment to regional control. More recently, the treatment of the axilla has evolved for women with macrometastatic axillary disease. Three randomized controlled trials have compared different regional treatment strategies for patients with > 2 mm of axillary tumor burden. Here we review the evolution of SLNB for the management of clinically node-negative breast cancer, and we address the current controversies and management issues.