Synthetic jet actuators and hybrid synthetic actuators are investigated in this book from both theoretical and experimental points of view. The main property observed for synthetic jet actuators is the frequency behavior of the velocity amplitude at the nozzle output of the actuator. This behavior was studied previously in many other publications; however, most of these papers have focused on actuators constrained by short stream-wise dimensions. Based on experiments, this book also describes the properties of actuators with longer stream-wise dimensions and introduces new mathematical models to characterize them. Hybrid synthetic jets are quite similar to synthetic jets, but they differ in the rectification of the flow in the nozzle. The rectification is achieved by additional fluidic diodes incorporated to the actuator. A measure of the flow rectification is the volumetric efficiency. This book introduces a new design for this kind of actuator that is tested experimentally; a very high volumetric efficiency is found at the second velocity resonance of the actuator.