Accelerated partial breast irradiation (APBI) is a new form of postlumpectomy radiotherapy delivered over 1 to 5 days. Early trials showed high local recurrence rates. More recent single and multiinstitutional studies, as well as a single phase III trial, have shown local control more comparable to whole breast radiotherapy. Patient selection and surgical technique are important variables preparatory to irradiation, which is delivered using 1 of 4 accelerated radiotherapy methods. Phase I/II studies have produced most of the information currently available regarding APBI. Additional phase III studies are underway to determine whether any or all of these accelerated radiotherapy approaches may safely substitute for whole breast radiotherapy in women seeking breast conservation.