The monograph covers all aspects of eukaryotic radiation genetics. The genetic effects of ionizing radiation at different levels of eukaryotic organization are considered - molecular, cellular, organizational, population, species. Particular attention is paid to the issue of determining the genetic risk of radiation for humans - the effect of high and small doses of radiation on human populations, determining the permissible levels of radiation, discussing the recommendations of the International Committee for Protection against Radiation of Different Years. Data on ways of protection of genetic structures of organism from mutagenic action of irradiation, on radioprotectors and mechanisms of their action are presented. Applied issues of radiation genetics are also covered - the use of the genetic effects of radiation in medicine, agriculture and industry.