Breast cancer is the most common malignancy among women in Korea. Over the past decades, the surgical treament of the breast cancer evolved significantly, and the trend has been towards less conservative approaches. The introduction of percutaneous image-guided biopsy has allowed less invasive diagnosis of nonpalpable breast lesions. Breast conservative therapy has become accepted as an alternative to mastectomy for more patients with ductal carcinoma in situ and early stage invasive brest cancer. Another major advance in the surgical treatment of breast cancer has been the development of the sentinel node biopsy procedure. This is a way to determine if the axilla is negative for metastases without a complete axillary dissection and its physical and functional complications. Since many patients today are diagnosed with early stage breast cancer and negative axillary nodes, this technique offers substantial benefit to numerous women.