This book on TENR discusses the basic Physics and Chemistry principles of natural radiation. The current knowledge of the biological effects of natural radiation is summarized. A wide variety of topics, from cosmic radiation to atmospheric, terrestrial and aquatic radiation is addressed, including radon, thoron, and depleted uranium. Issues like terrorism and geochronology using natural radiation are also examined. Comprehensive global TENR data assembly Critical assessment of the significant radiological impact of TENR on man and the environment as compared to radiological impact from man-made sources in nuclear technology and nuclear medicine Illustration of the importance of TENR for the future conceptual development of radiation protection.