This chapter briefly describes the basic elements of radiation therapy forms. Radiotherapy involves EBRT or brachytherapy or their combinations. Brachytherapy gives little radiation to surrounding normal organs. EBRT is developed from conventional 2D EBRT to 3D conformal radiotherapy, image-guided radiotherapy, intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT). High-risk patients are often treated with combinatory therapies in addition to radical prostatectomy and EBRT, such as androgen deprivation therapy (ADT). To understand EBRT is essential. Radiation therapy is used to either attempt to cure the prostate cancer or to help symptoms when a cure is not possible. This chapter reviews briefly methods for radiation therapy in prostate cancer. To understand EBRT is essential when image-guided radiotherapy is becoming more important and where target definition is most often based on PET.