© 1999 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Unsteady, viscous flowfields over a NACA0012 airfoil oscillated in plunge and/or pitch at various reduced frequency, amplitude and phase shift are computed. Vortical wake formations, boundary layer flows at the leading edge, the formation of leading edge vortices and their downstream convection are presented in terms of unsteady particle traces. Flow separation characteristics and thrust producing wake profiles are identified. Computed results compare well with the water tunnel flow visualization and force data, and other computational data. It is shown that the maximum propulsive efficiency is obtained for cases where the flow remains mostly attached over the airfoil oscillated in a combined pitch and plunge.