Radiobiology is a medical science that studies the response of cells and living systems to ionising radiation. Ionising radiation can be harmful to living systems. The mechanism of cell damage by ionising radiation involves physics, chemistry and biological processes. The cell repair mechanism after irradiation is important. Short- and long-term effects, either stochastic or deterministic, are important considerations in radiation effects on living systems. The study of radiobiology applies to radiation protection, industries that utilise radiation, in particular, clinical disciplines like diagnostic imaging, nuclear medicine and radiotherapy.