Breast-conserving therapy has been established as a standard treatment for women with early-stage breast cancer. Whole-breast irradiation has traditionally been utilized to consolidate local therapy following conservative surgery. Recently, the need for whole-breast irradiation after breast-conserving surgery has become controversial, with some investigators advocating accelerated partial breast irradiation as an alternative. Accelerated partial breast irradiation is delivered over a shorter period and only to a portion of the breast. This review will examine the emerging role of accelerated partial breast irradiation in the treatment of early-stage breast cancer and review the biologic rationale for, techniques of, and limitations of partial breast irradiation following breast-conserving surgery.