Radiotherapy has been widely used in breast cancer in many situations. These are breast irradiation of breast conserving therapy,post mastectomy regional irradiation,irradiation for regional lymph nodes recurrence,breast irradiation of inoperable locally advanced cases,palliative irradiation of brain metastasis,bone metastasis and so on. The relationship among radiotherapy,surgery and systemic therapy has to be considered in those situations. In breast conserving therapy, the usefulness of breast irradiation is well established. Otherwise, a local controllability depend on a grade of residual tumor cell has not been understand. The authors conducted the survey of 941 cases of positive surgical margins and found that doses more than 60 Gy has a tendency for better local control in post menopausal cases. To reduce patient's burden,3 weeks short course irradiation (Canadian protocol) or accelerated partial breast irradiation have been introduced in breast irradiation. A subgroup which has no need to irradiate to conserving breast had not been identified. The timing between postoperative chemotherapy and irradiation is another point that has to be considered. To reduce distant metastasis,chemotherapy first has been considered better. As for post mastectomy regional irradiation, improvement of local and systemic control has been widely known these days. A timing of systemic therapy and irradiation is a point has to consider. In inoperable or far advanced T 4 tumors, breast irradiation with concurrent chemotherapy must be considered in stead of surgery. We have to know a big shortage in Japanese cancer treatment situation that we have few radiation oncologists or medical physicists in Japan. We have to educate those specialists to catch up with increasing cancer patients.