Kudryashov (radiation biophysics, Lomonosov Moscow State U.) speaks not only from academic experience but also as a participant in the liquidation of the Chernobyl nuclear power plant. He concentrates here on primary and secondary processes of responses of living systems to radiation and the mechanisms of direct and indirect radiation through the involvement of water and lipids. He explains the characteristics of ionizing radiation and its dosimetry, the process of absorption of the energy of ionizing radiation, the absorbed dose and its biological effects, direct and indirection actions, the response of the cell to the action of ionizing radiation, and the long-term biological effects of low doses of ionizing radiation. Kudryashov expects his readership to include students of biology, physics, chemistry, radiation biology and medicine, professionals in ionizing radiation, and general readers living with increased background radiation.