Radon-222 is a radioactive gas of natural origin, primarily of telluric origin. It can accumulate in the more confined indoor air of buildings, where people spend an average of 90% of their time (70% of which is spent at home). This makes it one of the main sources of exposure to ionizing radiation for the general population in terms of its contribution to the annual dose. The results of animal experiments and, above all, epidemiological studies in humans show that the primary risk is lung cancer. Applying the exposure-effect relationships derived from monitoring cohorts of miners to estimates of domestic radon exposure in France makes it one of the main risk factors for this cancer after tobacco (approximately 13% of lung cancer deaths are attributed to radon in homes). However, this risk can be reduced by lowering radon levels in buildings through the adoption of technical measures now available for both new and existing structures. Radon is therefore one of the major public health issues in the field of ionizing radiation and, as such, a priority for action. It justifies the implementation of a management policy that, in this specific area, can benefit from objective characterizations of exposures and risks. First the Directorate General for Health, and then the Directorate General for Nuclear Safety and Radiation Protection, are leading a radon risk management policy in France. Several circulars (see Appendix II) define the actions of decentralized government agencies regarding radon in establishments open to the public, requiring, in particular, comprehensive measurement of this gas in such buildings across 31 departments. Based on Order No. 2001-270 of March 28, 2001, Decree No. 2002-460 of April 4, 2002 requires that, in these departments, the managers of certain public buildings conduct radon measurements and implement immediate measures to reduce public exposure to this gas if measurements exceed 400 Bq/m³.m-3 In parallel with the implementation of this policy, a number of actions have been undertaken; notably, the launch of regional awareness campaigns and radon measurements in residential buildings, supplemented by corresponding risk characterization. The result of these initiatives is a significant increase in the information available on radon. The challenge is to harmonize and support the production and centralization of this information to make it useful for guiding and monitoring risk management actions. The Ministry of Health (DOS) proposed to the Institute for Public Health Surveillance that it lead a discussion on this subject (see letter of March 12, 2001 in Appendix I). Conducted in consultation with organizations involved in measuring radon exposure and researching its associated effects, the objectives of this review were, after taking stock of existing knowledge and actions already undertaken, to define recommendations aimed at: - better characterizing radon exposure among the general population and children in buildings, so as to be able to conduct risk assessments for the general population, - develop, if necessary, new research on the health effects associated with radon exposure, - conduct risk assessments at the level of targeted populations