This chapter is concerned with Unmanned Aerial Vehicles (UAVs). A UAV is a remotely piloted or self-piloted aircraft that can carry a payload of cameras, sensors, communications, and electronic warfare equipment. A UAV may carry also a weapon, in which case it is called an Unmanned Combat Aerial Vehicle (UCAV). UCAV s are effective attack weapons. Typical missions of UAVs are surveillance , reconnaissance , target engagement, and fire control for other long-range weapons. UAVs vary in design, size, capabilities, and endurance. Small and lightweight UAVs, with limited endurance and flying range are used for close-range surveillance and reconnaissance by tactical units such as infantry battalions and special operations teams. Larger and heavier UAVs, with higher endurance and longer range, are used for longer reconnaissance missions such as gathering operational-level intelligence . At the far end of the line of UAVs stand very large vehicles that weigh several tons, can endure continuous missions of 24 h and more, and fly at a very high altitude (up to 20 km). The flying range of such UAVs is thousands of km, and their primary use is to provide wide area coverage for strategic information-gathering missions.