The efficacy of dielectric barrier discharge plasmas driven by high-voltage (∼16 kV) repetitive nanosecond pulses (∼60 ns full width at half-maximum) for flow separation control is investigated experimentally on an airfoil leading edge up to Re = 1 × 106 (62 m=s). Unlike alternating-current dielectric barrier discharges, the nanosecond-pulsedriven dielectric barrier discharge plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc-filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible from pulse to pulse. The device performs as an active trip at high-Reynolds-number prestall angles of attack and provides perturbations that generate coherent spanwise vortices at poststall. These coherent structures entrain freestream momentum, thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of F+c + 4-6 are most effective for control. Such devices, which are believed to function through thermal effects, could be an alternative to alternating-current dielectric barrier discharge plasmas, which rely on momentum addition.