Substantial progress has been made in modeling and understanding nonlinear aeroelastic phenomena. Experimental and theoretical investigations have shown good correlation for a number of nonlinear physical mechanisms. A number of physical mechanisms can lead to nonlinear aeroelastic response including the impact of static fluid or static structural nonlinearities in changing the flutter boundary of an aeroelastic system. The good news is that finite amplitude oscillations can in some cases replace what would otherwise be the rapidly growing and destructive oscillations of classical flutter behavior.