Abstract According to the World Health Organization (WHO) radon constitutes the second cause of lung cancer in the general population, the first being smoking. In addition health investigations also show that children are more susceptible than adults to ionizing radiation. In the past, it was accepted that only radon concentrations above 400 Bq/m3 could constitute a health risk, however, recent epidemiological findings demonstrate lung cancer risk from exposure to indoor radon at levels in the order of 100 Bq/m3. Furthermore, lung cancer aggravates based on the accumulated inhaled dose and, according to WHO, there is no lower radon level below which the risk from exposure disappears. Nevertheless, some surveys show that the majority of the public seems to consider the health risks involved in radon exposure as being negligible. To make things worse, only a few countries require the use of protection measures for buildings located in radon affected areas. This paper reviews literature on radon as a source of indoor air contamination. It covers recent legislation, building protecting measures and their cost-effectiveness. It also covers the case of radon emissions from construction and decorative materials.