High‐energy accelerators are not generally regarded as potential sources of significant environmental radiation or radioactivity. Indeed, by comparison with nuclear reactors, they produce rather small quantitiesofradioactivity, even though some kilocuries of radioactive material may be produced by some of these machines. The environmental impact of high‐energy accelerators is different in character from that of most nuclear installations. With accelerators, the predominant source of radiation exposuretothe general population is duetothe leakage of radionuclides into the environment. Studies of the production of the prompt radiation field during accelerator operation are reviewed, together with the transport of the field at large distances from the accelerator. Models for the calculation of population exposure are described and the experience at several high‐energy facilities summarized. Population exposure from radionuclides released to the atmosphere as a result of accelerator operation are at least an order of magnitude lower than that from prompt radiation — long‐lived radionuclides such as3H and7Be are of greatest concern. The production of radionuclides in soil and ground water near accelerators and their possible migration away from the accelerator site in ground water systems are thoroughly discussed. No significant population exposure is expected to arise from this source of environmental contamination at presently existing energies and intensities.