The papers collected in this book show the results of investigations performed by Russian scientists in the field of low dose irradiation action. It is confirmed that low doses do have effects on the human organism and the environment and that the most serious consequences are observed in the far post-irradiation period. This branch of radiobiology, which developed after the Chernobyl accident and studied its consequences, is discussed in detail. The main part of reviews and articles is devoted to the aspects of low dose effects on the human and animal genome and far post-irradiation consequences. New details of mechanisms of low dose action are shown and methods of their determination are discussed. Furthermore, the adaptive response of organisms and the low dose effects on the immune system are demonstrated. Also, the difference between protection mechanisms against low dose irradiation and against high dose irradiation is shown and proved.