There has been great interest in Europe in treating selected patients with early-stage breast cancer with accelerated partial breast irradiation (APBI) using interstitial brachytherapy. We review the results of these studies. Five early studies had local recurrence rates of 6% to 37%, reflecting suboptimal patient selection, target definition, and quality assurance procedures. Five more recent studies performed using much more stringent approaches have had recurrence rates of 0% to 7% with 84% to 92% of patients having excellent or good cosmetic results. The 3-year results of a single-institution phase III trial suggest that partial-breast brachytherapy performed in this manner yields local control that is very similar to that of whole-breast irradiation. Recently, a phase III multicenter protocol comparing these 2 modalities has been activated in Europe by the Breast Cancer Working Group of the Groupe Europeen de Curietherapie-European Society for Therapeutic Radiology and Oncology. As data from this and other trials mature, they will address and refine issues of patient selection, target volume definition, total dose, and fractionation and hopefully support the implementation of APBI into routine clinical practice.