“Passenger screening at commercial airports in the United States has gone through significant changes since the events of September 11, 2001. In response to increased concern over terrorist attacks on aircrafts, the Transportation Security Administration (TSA) has deployed security systems of advanced imaging technology (AIT) to screen passengers at airports. To date (December 2014), TSA has deployed AITs in U.S. airports of two different technologies that use different types of radiation to detect threats: millimeter wave and X-ray backscatter AIT systems. X-ray backscatter AITs were deployed in U.S. airports in 2008 and subsequently removed from all airports by June 2013 due to privacy concerns. TSA is looking to deploy a second-generation X-ray backscatter AIT equipped with privacy software to eliminate production of an image of the person being screened in order to alleviate these concerns. This report reviews previous studies as well as current processes used by the Department of Homeland Security and equipment manufacturers to estimate radiation exposures resulting from backscatter X-ray advanced imaging technology system use in screening air travelers. Airport Passenger Screening Using Backscatter X-Ray Machines examines whether exposures comply with applicable health and safety standards for public and occupational exposures to ionizing radiation and whether system design, operating procedures, and maintenance procedures are appropriate to prevent over exposures of travelers and operators to ionizing radiation. This study aims to address concerns about exposure to radiation from X-ray backscatter AITs raised by Congress, individuals within the scientific community, and others.”