Congress has expressed a great deal of interest in using Unmanned Aircraft Systems (UASs) to surveil the United States' international land border. This book examines the strengths and limitations of deploying UASs along the borders and related issues for Congress. Experts predict that UASs could perform some manned aircraft missions with less noise and fewer emissions. Thus, the potential uses for UASs, such as in hurricane research, law enforcement and real estate photography are also discussed. Furthermore, this book deals with the current and potential uses and benefits of UASs, as well as the challenges that exist in operating UASs safely and routinely in the national airspace system. To review these questions, GAO reviewed the literature, interviewed agency officials and aviation stakeholders and surveyed 23 UAS experts. This is an edited, excerpted and augmented edition of a CRS Report and GAO publication.