Book excerpt: Accelerated partial breast irradiation (APBI) is being rapidly introduced into the clinical management of early breast cancer. APBI, in fact, encompasses a number of different techniques and approaches that include brachytherapy, intraoperative, and external beam techniques. There is currently no single source that describes these techniques and their clinical implementation. This text is a concise handbook designed to assist the clinician in the implementation of APBI. This includes a review of the principles that underlie APBI, a practical and detailed description of each technique for APBI, a review of current clinical results of APBI, and a review of the incidence and management of treatment related complications.