<p><span style="color: rgb(51, 51, 51); font-family: Arial, Verdana, Helvetica, sans-serif; font-size: 12px;">Hypersonic vehicles attain a speed five times more high-speed than the speed of sound, which is beyond Mach 5 and nearly equal to 6174km/h. Hypersonic flow has certain characteristics, essentially a reedy shock layer, formation of entropy layer, viscous interactions, high temperature, and low-density flow. Only if these characteristics are subjected in the flow can the flow can be called hypersonic. While designing a hypersonic flight vehicle, the characteristics of the hypersonic atmosphere should be understood clearly. This comes as a major design constraint. A brief overview of the hypersonic vehicle design and high-speed flow characteristics will be presented in this chapter. A few characteristics of hypersonic flow and the ideal design conditions will also be reviewed.</span><br></p>