This thesis investigates the wake response of rectangular prisms to synthetic jets driven at a constant frequency. The purpose of this investigation is two-fold. First, to determine the difference in the wake response of rectangular prisms with thickness-to-chord ratios in different dynamic regions. Second, to determine how perturbations of the shear layer affect the vortex shedding response. To this end, the actuator is placed at the leading edge of the obstacle. Experiments were conducted on two geometries (thin-plate: B/D = 0.3, square: B/D = 1.0) in a small-scale wind tunnel. The actuation frequency was varied across a wide range of frequencies and only the pressure response was recorded. This was done for three separate Reynolds numbers, 8000, 10000, and 12000. Cases at select actuation frequencies were chosen for particle image velocimetry experiments. These were conducted at Re = 8000 and 10000 for the thin-plate and square prism, respectively. The thin-plate showed a relatively insensitive response to actuation. The mean coefficient drag was increased with increasing actuation frequency, and there was no effect on the Strouhal number. In contrast, the square prism showed a varied response. The coefficient of drag generally decreased and varied rapidly from a local maximum to a local minimum in synchronization bands. The Strouhal number showed a rapid variation between a local minimum and a local maximum in the synchronization bands. Between these synchronization bands, the St had a step-like increase relative to the baseflow. This difference in the response was attributed to the presence of the afterbody. The characteristics of the wake response to shear layer perturbation were investigated for the square prism. The different observed flow con figurations were due to when the actuation pulse interacted with the shedding cycle. For the synchronized flow cases, the difference across the synchronization band was due to a phase difference in the actuation pulse relative to the shedding cycle. The mechanism in which the actuator influenced the shear layer was predominately via the decay of vorticity in the shear layer via cross-diffusive annihilation. Changes in the St were shown to be from a modification of the circulation density.