Breast cancer is most common cancer in women in Korea from 2002. Early diagnosis is important to the treatment and the survival of patients. Clinical examination, imaging study, and pathologic examination are essential for diagnosis of breast cancer. Mammography and clinical breast examination have been widely used for screening. However, additional examination like ultrasonography is usually needed due to low sensitivity of mammography to the dense breast as found in many Korean women. The role of ultrasonography and MRI as a screening tool is controversial. Definite diagnosis of breast cancer is confirmed by pathologic review of breast tissue. A palpable lesion can be excised surgically or biopsied with fine-needle aspiration or core needle biopsy. Nonpalpable lesions can be excised surgically with needle localization or biopsied with core needle biopsy or vaccum assisted biopsy under radiologic guidance. For early detection and precise diagnosis of breast cancer, clinical history, physical examination, radiologic imaging and pathologic review should be balanced. The recommendations of screening and diagnostic tools for breast cancer are discussed in this article.