In radiation-induced carcinogenesis the stages of initiation, transformation, and promotion can be identified. Radiation carcinogenesis is a stochastic phenomenon that does not exhibit any threshold in the dose-response relationship. The most important risk to be controlled is that of the population--either industrial or medical--exposed to radiation at low levels and low dose rates. Despite the expanding use of radiation, the average doses in most industrialized societies have not been increasing during the last few years. However, sensitive subpopulations with high cancer risks are included within the present low-level average exposure figures.