Book excerpt: When discussing the risk of introducing drones into the National Airspace System, it is necessary to consider the increase in risk to people in manned aircraft and on the ground as well as the various ways in which this new technology may reduce risk and save lives, sometimes in ways that cannot readily be accounted for with current safety assessment processes. This report examines the various ways that risk can be defined and applied to integrating these Unmanned Aircraft Systems (UAS) into the National Airspace System managed by the Federal Aviation Administration (FAA). It also identifies needs for additional research and developmental opportunities in this field.