Sentinel lymph node (SLN) biopsy is standard care for patients with cN0 breast cancer, and SLN-negative patients do not require axillary dissection (ALND). It is now clear that many patients with positive SLN do not require ALND. In ACOSOG Z0011, 6-year locoregional control and survival (in cT1–2N0 patients with ≤2 positive SLN treated by breast conservation and whole breast radiotherapy) were comparable for SLN biopsy alone compared to SLN biopsy plus ALND. A growing body of data now suggests that ALND may not be required for selected patients outside the Z0011 eligibility criteria, including those treated with neoadjuvant chemotherapy (NAC). Retrospective and prospective studies confirm that the success of SLN biopsy after NAC is slightly lower and the false-negative rate slightly higher than those of SLN biopsy in general. The performance of SLN biopsy after NAC is optimized by the use of combined dye–isotope mapping and by the removal of at least two SLN. After NAC, ALND remains standard care for those who remain SLN-positive but may not be required for SLN-negative patients. Future trials will focus on patients with proven axillary node metastasis prior to NAC, and ask whether axillary radiotherapy is required for those who become SLN negative, and whether ALND is required for those who remain SLN-positive.