A review of the behaviour of radon in the geological environment is presented. The general geochemistry of the element is described and the factors controlling its emanation from minerals and rocks and into the disperse phases itemized. A brief summary of analytical procedures for the analysis of the radon isotopes in waters and soil gases is given. The emanation of radon depends upon the source term uranium concentration, the nature of the host mineralogy, the permeability of the host rock and soil and the characteristics of the transporting medium. Weather can have a profound effect upon the concentration of radon in soil gas but often the variation due to the geological substrate is greater. Radon is not a problem unless it collects in buildings and underground structures. Some guidelines are given for identifying areas of high radon emanation based upon existing data sets.