Exposure to indoor radon is known to be one of the main risks of ionizing radiation. It is estimated that tens of thousands of deaths globally occur per year due to the lung cancer. Many national authorities have therefore put in place large monitoring campaigns to delineate those areas that are at risk. Besides radon, naturally occurring radionuclide in soil and building materials is another source of radiation exposure to the general public. Therefore, assessment of gamma radiation dose from natural sources is also of particular importance. Consequently, millions of radon and natural radioactivity related measurements have been made worldwide and reported in the open literature. The current book deals with the experimental studies concerning measurement of indoor Radon in different seasons. The radiological hazards associated with indoor radon and natural radioactivity present in soil and building materials are also dealt with in greater details. A comprehensive review of the radon related studies carried out in Pakistan, measurement of radon exhalation rate from the samples of soil and building materials and its dependence on moisture content are also included in this book.