The Air Force is pursuing the development of hypersonic boost-glide and air-breathing missiles, and considering the development of platforms for rapid response and intelligence, surveillance, and reconnaissance (ISR) applications. These development programs are motivated by the increasing defensive and offensive capabilities of our potential adversaries. One of the most promising approaches involves platforms with air breathing supersonic combustion ramjet (scramjet) engines. The air breathing capability leads to greater range and more effective payload utilization. The development of these platforms presents a significant challenge, both for the design and for testing and evaluation. At speeds exceeding Mach 5, overcoming the drag requires scramjet engines and aerodynamic platforms that operate very close to the margin, so avoiding catastrophic failures is a major concern. Heat fluxes are in the megawatts per square meter and engine “unstart” can occur in tens of milliseconds. The first manned hypersonic flight was achieved in 1967 with the Mach 6.72 flight of the rocket-propelled X-15, but realistic air breathing hypersonic platforms were not considered viable until the final and successful flight of the X -51 in 2013. Now the challenge is to field an affordable and effective air launched hypersonic missile within the next decade and a ground takeoff and return hypersonic ISR capability following that. This talk will focus on the technical challenges associated with development and testing of air breathing hypersonic vehicles.