The most extensively studied radiation-resistant bacterium is Deinococcus radiodurans. Several radiation resistance mechanisms possessed by this bacterium have been elucidated at the molecular level. In contrast, microorganisms other than D. radiodurans exhibit resistance to ionizing radiation. Various radiation-resistant bacteria have been isolated from groups that are evolutionarily close to Deinococcus as well as those that are evolutionarily distant from it. In addition, some archaea are resistant to radiation. For applications in the biotechnology industry, research is being conducted to utilize radiation-resistant bacteria as hosts or harness the genes they possess, and further research and development are anticipated.