Any active flow control system necessarily includes actuators. The modeling, design, fabrication, and testing of these devices can be complicated, expensive, and time consuming, often requiring numerous design cycles with less than satisfactory results. The purpose of this chapter is to review recent progress in popular actuators for flow control applications. A brief discussion of basic terminology and design specifications is provided first, followed by their specific interplay with potential flow control objectives. There are numerous types of actuators, and time does not allow a comprehensive discussion of all of these. Therefore only the most popular or promising are discussed after beginning with some historical perspective. In addition, a section is included on actuators potentially suitable for high-speed flows. In all cases, we attempt to summarize key advantages and disadvantages of each, along with unresolved research issues. Suggestions for metrics to consider when using actuators in active flow control applications are also provided.