An increasing number of centers, having completed validation studies of SLN biopsy, offer patients the option of no further axillary surgery if the SLN is negative. Despite this encouraging debut, SLN biopsy is a new operation, has a definite learning curve, and is highly multidisciplinary, requiring the cooperation of nuclear medicine physicians, surgeons, and pathologists. The techniques pertinent to each specialty continue to evolve, and many of these aspects remain the subject of debate.