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The temporal dynamics of large-scale structures in a plane turbulent mixing layer are studied through the development of a low-order dynamical system of ordinary di erential equations (ODEs). This model was derived by projecting the Navier{Stokes equations onto an empirical basis set from the Proper Orthogonal Decomposition (POD) using a Galerkin method. To obtain this low-dimensional set of equations, a truncation is performed including only the rst POD mode for selected streamwise/spanwise (k 1 =k 3) modes. The initial truncations included only k 3 = 0. Once these truncations were evaluated , non-zero spanwise wavenumbers were then added. These truncated systems of equations are then examined in the pseudo Fourier space in which they are solved and by reconstructing the velocity eld. Two di erent methods for closing the mean streamwise velocity are evaluated to show the importance for the dynamical representation of the ow to introduce in the low-order dynamical system a term allowing for feedback between y Present address: 2 Ukeiley et al. the turbulent and mean ows. The results of the numerical simulations showed a strongly periodic ow indicative of the spanwise aligned vorticity. The simulated ow had the correct energy distributions in the cross-stream direction. These models also indicated that the events associated with the centre of the mixing layer lead the temporal dynamics. For truncations involving both spanwise and streamwise wavenumbers the reconstructed velocity eld exhibited the main spanwise and streamwise vortical structures known to exist in this ow. The streamwise aligned vorticity was shown to connect spanwise vortex tubes.