Lymphatic mapping and biopsy of the sentinel lymph nodes (SLNs) as a method for pathologically staging breast cancer patients has been extensively evaluated over the past 10 years. The goal of this approach is to stage patients accurately in order to make appropriate decisions about adjuvant treatment, but also to avoid the potential morbidity of conventional axillary lymph node dissection (ALND). A large number of single center and multicenter trials have been reported that indicate the accuracy of several different methods, and the largest prospective randomized trial of SLN biopsy versus ALND, conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP), completed accrual last year. Other trials with different designs and objectives have also been completed. A great deal of information is now available on the use of this approach to breast cancer staging, but many questions remain controversial, including technical issues and patient selection parameters.