Sentinel lymph node (SN) biopsy for breast cancer has been introduced in the mid-1990s and it has now been performed on thousands of patients. This procedure has been rapidly adopted around the world by surgical specialists in clinical practice as a diagnostic procedure instead of the axillary lymph node dissection. The diffusion of the SN mapping in routine must be careful by respecting some principles of methodology and especially of training, in order to maintain its irreversible development. However, the advent of this mini-invasive technique revealed new questions, which the concept of the SN procedure raises: can we increase the current indications? Could axillary lymph node dissection be avoided in patients with metastatic SN? What is the morbidity of the biopsy of the SN? Which is the prognostic value of micrometastatis discovered by the diffusion of the ultra-stadification of the SNs? The GS procedure is a diagnostic method the reliability of which is now on accepted in its usual indications (tumours in place, small size breast tumour without palpable adenopathy). The value of the axillary dissection after metastatic SN is the subject of debates and controversies although axillary dissection remains recommended. So the use of scores or predictive nomograms is currently developed to select the patients being able not to justify of complementary axillary dissection, and seems promising.