Since the last edition of this textbook, interventional radiation therapy (brachytherapy) has undergone significant developments. The incorporation of advanced image-guiding procedures and the establishment of new applicators allow for the highly accurate implantation of complex implants. 3D-guided real-time adaptive brachytherapy is becoming the newest clinical standard. We now find ourselves in an exciting “new era” of brachytherapy. The current edition of this textbook has been updated to include all these new developments in brachytherapy, including the results of recent clinical trials and updates to the brachytherapy guidelines by the European Brachytherapy Group within ESTRO (GEC-ESTRO). A number of highly experienced authors and skilled colleagues from all over Europe have contributed to this edition to educate and inspire all members of the radiation oncology team to utilise the full potential of brachytherapy to the benefit of their patients.