Sentinel lymph node biopsy (SLNB) is standard care for patients with early-stage breast cancer, and axillary lymph node dissection (ALND) is considered unnecessary when sentinel lymph nodes (SLNs) are tumor-free. Additional non-SLN metastasis in patients with positive SLNs can be estimated using several risk factors such as primary tumor size, metastatic tumor size in SLNs, lymphatic vessel invasion, and so on. All patients with positive SLNs may be treated with further ALND based on their own risk for non-SLN metastasis. Recent randomized clinical trials have already proved less surgical morbidity and better QOL for SLNB alone compared with ALND. However, trials concerning the efficacy of ALND in positive SLNB patients in preventing local regional recurrence and improving overall survival compared with no ALND, and also, concerning the effectiveness of ALND compared with axillary radiation therapy (RT), have not yielded clear results. The prognostic significance of micrometastasis in SLNs or bone marrow also remains to be determined. So far SLNB is not acceptable for patients with positive nodes in the axilla at initial diagnosis even if their axillary metastases are down-staged to negative by neoadjuvant chemotherapy. Although basically SLNB does not need to be performed for patients with pure ductal carcinoma in situ (DCIS), it is recommended for patients with an initial diagnosis of DCIS which is large, palpable, high grade, or found in younger patients. Because these types of DCIS have higher incidences of accompanying invasive lesions. In addition if patients will undergo mastectomy, SLNB is recommended because of the inability to perform SLNB after mastectomy. SLNB may be acceptable for patients with T3 or T4b tumors, even though SLN identification is lower yet SLN involvement is higher compared with T1 or T2 tumors, and systemic adjuvant therapy is more important for patients with T3 or T4b tumors. SLNB is a bridge to further axillary treatment such as ALND or axillary RT, and which strategy, including no further treatment, is best considered individually based on recurrence risk, treatment responsiveness and use or non-use of systemic therapy.