The representation of unsteady aerodynamic e owe elds in terms of global aerodynamic modes has proven to be a useful method for reducing the size of the aerodynamic model over those representations that use local variables at discrete grid points in the e ow e eld. Eigenmodes and proper orthogonal decomposition modes have been used for this purpose with good effect. This suggests that system identie cation models may also be used to represent the aerodynamic e owe eld. Implicit in the use of a systems identie cation technique is the notion that a relative small state-space model can be useful in describing a dynamical system. The proper orthogonal decomposition model is e rst used to show that indeed a reduced-order model can be obtained from a much larger numerical aerodynamical model (the vortex lattice method is used for illustrative purposes ), and the results from the proper orthogonal decomposition model and the system identie cation methods are then compared. For the example considered the two methods are shown to give comparable results in terms of accuracy and reduced model size. Theadvantagesand limitationsofeachapproacharebriee y discussed.Both appearpromisingandcomplementary in their characteristics.