A series of flutter model tests were conducted in the Mach number range 5 to 8 to provide flutter trends and evaluate theoretical flutter prediction methods. The tests were on rectangular planform models in AEDC Tunnel E-2. Experimental results were obtained on flutter effects from varying Mach number, uncoupled frequency ratio, center of gravity, thickness ratio, profile shape, and aspect ratio. Results and trends, presented in terms of flutter velocity index, are compared with flutter data predicted by piston theory aerodynamics. Interesting results concerning the effects of structural damping on hypersonic flutter characteristics and relative flutter characteristics for hypersonic and lower speed ranges are presented. Using piston theory for predicting hypersonic flutter speeds is evaluated, and improvements in theoretical procedures are discussed.