Radiobiology as a subject -- A historical background -- Radiosensitivity -- Physical characteristics of Ionizing Radiations -- Direct and indirect effects of IR -- Response of cells to irradiation. Cell radiosensitivity -- Modification of radiosensitivity. The oxigen effect -- RBE of IR -- Mechanism of the biological effect of IR -- Radiosensitivity of tissues, organs and organism. Radiation syndromes -- Radiation sickness in man -- Recovery proc. in an irradiated organism -- The biological effect of incorporated radionuclides -- Indirect irradiation effects. Impairment of metabolism and changes in non-critical systems of an organism -- Late effects of irradiation -- Effects of radiation on the embryo and fetus -- Safety standars of IR -- Therapy of acute radiation sickness -- Biological radiation protection of an organism -- Radiobiological fundamentals of the therapeutic application of IR -- To the young researcher