We present the application of orthogonal wavelet filtering to study mixing and chemical reaction in 2D turbulent flows. We show that the coherent vortices are responsible for the mixing dynamics. Therefore, we perform direct numerical simulation of decaying and statistically stationary homogeneous isotropic 2D turbulence. We split the flow in each time step into coherent vortices represented by few wavelet modes and containing most of the kinetic energy and an incoherent background flow. We quantify the mixing properties of both flow components and demonstrate that efficient mixing of scalars is triggered by the coherent flow, while the influence of the incoherent flow on the mixing corresponds to pure diffusion. These results hold for both passive scalars and reactive scalars with simple and multi-step kinetics. (C) 2003 Elsevier Science Ltd. All rights reserved.