Safegrounds is a forum for developing and disseminating good practice guidance on the management of radioactively contaminated land on nuclear and defence sites in the UK. This review has been provided to Safegrounds as a summary of the basis for current radiation risk estimates and the International Commission on Radiological Protection (ICRP) protection system, in a form that will be accessible to a wide range of stakeholders. Safegrounds has also received viewpoint papers from other members who contend that the ICRP methodology results in substantial underestimates of risk, particularly for internal emitters. There is an extensive literature on the risks of radiation exposure, regularly reviewed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and other expert groups. These data provide a sound basis for the system of protection recommended by ICRP. The available epidemiological and experimental evidence supports the application of cancer risk estimates derived for acute, high dose, external exposures to low dose exposures to external and internal sources. In the context of radioactively contaminated land on nuclear and defence sites, the national standards for the cleaning up of land and for waste disposal correspond to very low doses, two orders of magnitude less than average annual doses in the UK from natural background radiation (10-20 νSv compared with 2-3mSv). Risks at such very low doses can only be estimated on the basis of observations after exposure of population groups at much higher doses. The estimated risks at these very low doses, while uncertain, are as likely to be overestimates as underestimates.