Timing is essential to our economic and national security. It is needed to synchronize networks, for digital broadcast, to efficiently use spectrum, for properly ordering a wide variety of transactions, and to optimize power grids. It is also the underpinning of wireless positioning and navigation systems. America’s over-reliance for timing on vulnerable Global Positioning System (GPS) signals is a disaster waiting to happen. Solar flares, cyberattacks, military or terrorist action – all could permanently disable space systems such as GPS, or disrupt them for significant periods of time. Fortunately, America already has the technology and components for a reliable and resilient national timing architecture that will include space-based assets. This system-of-systems architecture is essential to underpin today’s technology and support development of tomorrow’s systems. This paper discusses the need and rationale for a federally sponsored National Timing Architecture. It proposes a phased implementation using Global Navigation Satellite Systems (GNSS) such as GPS, eLoran, and fiber-based technologies. These were selected because they: • Provide maximum diversity of sources and least common failure modes, • Are mature, have repeatedly been demonstrated to perform at the required levels, and are ready to deploy, • Have the potential for further development to increase accuracy, resilience, and cyber security, • Are already supported, to varying degrees, by existing infrastructure, and • Require relatively modest investments.