Background: Breast-conserving surgery followed by radiation therapy with or without endocrine treatment leads to very high cure rates in early breast cancer. Objective: The aim of this article is to summarize the current standard of care in radiation therapy of early breast cancer as well as approaches for treatment optimization that are currently being tested in clinical trials. Material and methods: The indications, fractionation, standard doses and radiotherapy techniques as well as approaches of de- escalation, in particular for partial breast irradiation are described. Results: Conventional fractionated or hypofractionated whole breast irradiation with subsequent boost in the region of the former tumor is the current standard treatment after breast-conserving surgery of early breast cancer. In order to keep the boost volume and thus the risk of chronic toxicity as low as possible, the tumor bed must be carefully marked with clips by the surgeon. This becomes even more relevant when using partial breast irradiation schedules, which are currently being evaluated in clinical trials as a way of de-escalation of radiation therapy. Conclusion: The very high cure rates in early breast cancer steer the interest of researchers more and more to strategies for de-escalation of radiation therapy as well as to further reduction of chronic side effects. Partial breast irradiation or the omission of radiotherapy for patients with very low risk of recurrence are procedures that are currently being evaluated in clinical trials.