This chapter considers the anatomy of the clavipectoral fascia which is key to understanding axillary lymph node dissection. There is discussion of the quadrangular space, the triangular interval and the triangular space. The axillary contents are discussed as are the limits (and muscles involved) of the axilla. There is a section on the basic anatomy of the breast, the groupings of axillary lymph nodes and their dissection and the sentinel lymph node concept as it applies to breast cancer.