Radon is a natural decay product of uranium in the soil, with radium as an intermediate decay product. It was first identified as a health hazard in underground mines. Some of the most-exposed uranium miners had lung cancer rates as high as 40 percent. Radon problems in homes were first identified in the mid 1970s in homes built on or near uranium mill tailings, but it was thought not to be a widespread problem at the time. This changed in 1984 when a house in Pennsylvania was found to have extremely high radon levels from natural radium formations. Since then, radon has been found to be a nationwide problem. This talk will describe the nature and extent of the radon problem, the measurement techniques for radon, and the methods used to prevent radon from entering a building. The talk will emphasize the science of radon control. The involvement of government will be addressed in only response to questions from the audience.