Introduction - the significance of radiobiology for radiotherapy the growth of tumours cell proliferation in tumours proliferative and cellular organization of normal tumours radiation response and tolerance of normal tissues clonogenic cells and the concept of cell survival models of radiation cell killing DNA damage and cell killing genetic control for the cellular response to ionizing radiation dose-response relationships in radiotherapy clinical manifestations of normal-tissue damage time-dose relationships in radiotherapy the linear-quadratic approach to fractionation and calculation of isoeffect relationships hyperfractionation and accelerated radiotherapy the oxygen effect overcoming hypoxic radioresistance the radiobiology of tumours the dose-rate effect - brachytherapy particle beams in radiotherapy combination of radiotherapy and chemotherapy - principles combination of radiotherapy and chemotherapy - clinical application and evaluation re-treatment tolerance of normal tissues hyperthermia targeted radiotherapy individualization of radiotherapy.