The character of warfare has changed over time. Indeed, developments may be so dramatical that they can be characterized as revolutionary. Technology has developed new vehicles to attack enemies. This book elaborates on the Unmanned Aircraft System (UAS), also known as drones and UAV's (Unmanned Aerial Vehicle). It examines what the UAS is and what the legal limits are of the use of unmanned systems. The book looks at the lawful conflicts between nations based on the United Nation charter, as well as international humanitarian law of war based on the first Geneva protocol. Moreover, the legality of targeted killing with the use of unmanned systems is discussed.