<p/><br></br><p><b> About the Book </b></p></br></br>The authors assess the costs associated with realistic threats to domestic, nonmilitary uses of the Global Positioning System (GPS), and consider possible additions to the positioning, navigation, and timing ecosystem in light of those costs.<p/><br></br><p><b> Book Synopsis </b></p></br></br>Because of the widespread use of the Global Positioning System (GPS) for positioning, navigation, and timing (PNT), concerns have been expressed that a disruption of GPS might require a national investment in backup capabilities. The authors assess the costs associated with realistic threats to domestic, nonmilitary uses of GPS, and review possible additions to the PNT ecosystem in light of those costs.