We are constantly bathed in ionizing radiation from galactic and local sources. The earth, air, food, houses, clothing, and our bodies are radioactive. Radiation was undoubtedly active in the formation of biologically important molecules in prebiotic ages. Much adaptation for metabolic stability and genetic continuity of early life forms must have occurred in response to intense cosmic radiation before photosynthesis provided a protective canopy of oxygen and ozone around the earth. A positive attitude toward low doses of ionizing radiation is potentially beneficial to the development of a technologic society. Agricultural uses of ionizing radiation include decreased sprouting of potatoes and onions, insect sterilization, and food sterilization in some countries. The most general effect of high-energy radiation in biologic media is due to ionization. Irradiation has been used in microbiology as a tool to kill bacteria and to obtain mutated organisms.