Consider an airfoil which is impulsively started from rest to a constant speed relative to an otherwise quiescent fluid at an angle of attack. The paper attempts to propose a precise definition for the ‘‘starting vortex’’ in viscous flow and investigate how an airfoil gains its lift through the starting vortex. It is found adequate to view the vortex itself as a source of the lift through the vorticity contained within it. Actually, the total lift on the airfoil is contributed by all the regions of nonvanishing vorticity in the flow. For an impulsive flow, the initial lift is due to the vortex sheet distributed along the airfoil; the lift is then rapidly dominated by the starting vortex near the trailing edge. In the next stage, the regions of vorticity next to the airfoil on both sides gradually become the major contributor to the lift. Relative importance of the starting vortex is assessed based on the angle of attack and the Reynolds number.