In the early 2000s two landmark trials, the Ontario Clinical Oncology Group trial and START-B trial, established that hypofractionation of 40–42.5 Gy in 15–16 fractions over 3 weeks after breast conserving surgery or mastectomy resulted in similar rates of local recurrence and normal tissue effects. This led to a new standard for postoperative whole breast and chest wall radiation therapy. Further trials confirmed these findings and suggested that hypofractionation can be applied to patients in all subgroups, including with DCIS only or those requiring lymphatic irradiation. UK investigators have evaluated 5-fraction hypofractionation given over 1 week. In 2020 the FAST-Forward trial reported that 26 Gy in 5 fractions over 1 week was non-inferior to 40 Gy in 15 fractions in 3 weeks for local recurrence at 6 years and that late effects were similar between fractionation schedules. The UK adopted 26 Gy in 5 fractions in 2020 as a new standard for breast or chest wall radiation therapy, some other countries are following this approach. In addition to improvement in convenience and reduction in resources required, hypofractionation provides important benefits with respect to acute and late toxicity that can improve the quality of life of patients receiving breast radiation therapy.