The recent decision of the United Nation Scientific Committee on the Effects of Atomic Radiation to publish its report on beneficial (or hormetic) effects of small doses of radiation, which is based on a principle of linear-non-threshold dose-effect relationship. The hormetic effects were obserwed at biochemical, cellular and organism level in cellular cultures, bacteria, plants, experimental animals and in human populations. The most from among more than 1000 puublications on radiation hormesis are reviewed in the UNSCEAR report, in which the main emphasis is laid on elucidation of the mechanism of this phenomenon.