Breast conservation treatment (BCT) is a combination of breast conservation surgery (BCS) and radiotherapy (RT). Conventional radiotherapy after BCS requires 5~6 weeks of RT to whole breast followed by 1~2 weeks of RT to tumor bed. This lengthy tretment modality is one of the difficulties in performing BCT. Recently, irradiation to the tumor bed only (partial breast irradiation, PBI) in selected patients was examined as a way to shorten the period of RT because a local recurrence after a BCT occurs mainly around the primary tumor bed. PBI with a large fractional dose might shorten the treatment time to one week. There are various methods of PBI including interstitial brachytherapy, balloon brachytherapy, external beam radiotherapy such as three-dimensional conformal radiotherapy, intensity modulated radiotherapy and proton therapy, and intraoperative radiotherapy. The results of the phase I/II studies using these new techniques have reported a similar local control rate and cosmetic results compared with the historical data using whole breast irradiation (WBRT). However, a long-term follow-up of the phase III randomized trials will be needed in order to determine the equivalence of PBI alone to WBRT in the treatment of selected patients with early breast cancer.