Prior to 2012, unmanned aircraft systems (UAS) technology had been primarily used by the military and hobbyists, but it has more recently transitioned to broader application, including commercial and scientific applications, as well as to expanded military use. These new uses encroach on existing structures for managing the nation's airspace and present significant challenges to ensure that UASs are coordinated safely and suitably with existing manned aircraft and air traffic management systems, particularly with the National Airspace System (NAS). Of particular concern is the interaction between human pilots, operators, or controllers and increasingly automated systems. Enhanced understanding of these interactions is essential to avoid unintended consequences, especially as new technologies emerge. In order to explore these issues, the National Academies of Sciences, Engineering, and Medicine organized a 2-day workshop in January 2018. This publication summarizes the presentations and discussions from the workshop.