The most noteworthy recommendation of the 2009 WHO Handbook On Indoor Radon - A Public Health Perspective (see http://www.who.int/ionizing_radiation/env/radon/en/) is that country reference levels for radon should be set at 2.7 pCi/L (picocuries per liter), if possible, or as-low-as-reasonably-achievable, or ALARA, but should not exceed 8.1 pCi/L. This recommendation does not directly affect EPA?s current 4 pCi/L radon action level since: EPA has been recommending for years that homeowners should also consider fixing their homes when the radon level is between 2 and 4 pCi/L; since there is significant risk at levels below 4 pCi/L and there is no known ?safe? level of radon exposure. The WHO Handbook states that countries with radon programs and reference levels in the 2.7-8.1 pCi/L range, should consider reducing their reference level only AFTER improving their testing and fixing rates, which could save many more lives. The launch of the WHO Handbook On Indoor Radon in 2009 is a historic milestone in the history of world health and the risk from exposure to radon in indoor air. It is the FIRST Global Call to Action on indoor radon. Thirty countries and over 100 experts participated in reviewing the available science. Consensus was reached that radon in homes is a leading cause of lung cancer worldwide, with up to 14% of all lung cancers attributable to indoor radon. The Handbook is a guide for countries on starting or improving a national radon program. The WHO action is an unprecedented step of great significance toward reducing the number of radon-related lung cancers worldwide. Download the PDF version of the WHO Handbook at http://www.who.int/ionizing_radiation/env/9789241547673/en/ For more information on radon's health risks, visit https://19january2021snapshot.epa.gov/radon/health-risk-radon.