A lumped vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past tandem pitching airfoils. The unsteady wakes of both airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled flow is solved using a combined "zero-normal flow" boundary condition and Kelvin condition which results in (2N+2)X(2N+2) equations. Commercial software FLUENT is also used to study the flow tandem pitching airfoils. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the tandem airfoils pitching in or out of phase and also when only the leading airfoil pitches and the trailing airfoil is stationary. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.