Axillary lymph node status is the most important pathological determinant of prognosis in early breast cancer. Determination of axillary status is crucial in clinical decision-making. It is currently accepted that the total axillary lymphadenectomy is the most reliable staging procedure. However, routine axillary dissection does not benefit a majority of early breast cancer patients who are node-negative, and the patients sustain the potential morbidity and the economic cost of this procedure. There is substantial evidence that there is an orderly progression of breast cancer metastases in a lymphatic basin, sentinel node being the first node to receive lymphatic drainage from the tumor site. Sentinel lymph node biopsy may prove to be the optimal sampling technique for staging of breast cancer patients. A large multicenter trial to study the clinical validity of sentinel lymph node biopsy in breast cancer is underway. This paper addresses the rationale for sentinel lymph node biopsy and discusses the technical issues with regard to anatomy and physiology of breast lymphatics.