As we find ourselves bearing witness—even in our own backyards—to what is increasingly being referred to as the “drone revolution,” it might be a good time to turn our attention back in time and figure out how, exactly, we got here. The large-scale use of drones for national defense and law enforcement is a relatively recent development, but unmanned aerial surveillance draws from a doctrine that is as old as flight itself. Though the fundamental logic of aerial surveillance has remained the same—to put an eye in the sky so that one may look down upon one’s enemies—the technology has evolved dramatically over this period, driving shifts in aerial surveillance theory and practice. New technologies enable new techniques that, in turn, inspire new ways of thinking about how to spy from the sky, and produce new experiences for those being watched. Our present drone revolution, which has itself driven what is being called the “intelligence, surveillance, and reconnaissance (ISR) revolution,” is the result of this process played out over an entire century. The unmanned aerial spying efforts of the United States military and intelligence community have a particularly long and influential history, beginning with the Union Army’s manned observation balloon corps of the Civil War. Our story begins, in earnest, with fragile and failure-prone “aerial torpedos” in the First World War and an innovative and overlooked live video transmission system from the 1930s, through the CIA’s little-known—and radically forward-thinking—Samos spy satellite program of the late 1950s and a series of extraordinarily ambitious Cold War drone programs, up to the adoption of drones over Bosnia in the 1990s. Together, these episodes show how we got the drones of today and realized the core principles that define aerial spycraft (that is, how to find and watch “the bad guys”) in the 21st century: cover as much ground as possible; process and disseminate what you collect as quickly as possible, ideally, as close as you can get to real-time; and be as persistent as possible. The drones and high-resolution aerial cameras that are finding their way into the tool-kits of police departments will bring these principles along with them. Even if the growing number of law enforcement officers now using this technology aren’t fully aware of the long legacy of aerial surveillance that they are joining, the influence of this formative history of surveillance on their aerial crime-fighting operations is evident. Just as aerial surveillance transformed the battlefield, it will have a similarly profound effect on the experience and tactics of those operating the cameras, as well as, crucially, those individuals being watched by them. By grasping this history, we can better understand not only why and how drones are being used to fight crime, but also what to expect when every police department in the country owns an eye in the sky.