Commercial interest for unmanned aircraft systems (UAS) has seen a steady increase over the last decade. Nevertheless, UAS operations have remained almost exclusively military. This is mainly due to the lack of a regulatory framework that allows only limited public and civil UAS operations with usually crippling restrictions. Although efforts from the Federal Aviation Administration and its partners are already underway to integrate UAS in the National Airspace System (NAS), the appropriate regulation will not be ready for several more years. In the meantime UAS developers need to be aware of the current operational restrictions, as well as make informed decisions on their research and development efforts so that their designs will be airworthy when the regulatory framework is in place. This monograph aims to present an overview of current aviation regulation followed by an investigation of issues and factors that will affect future regulation.