The modern UFO phenomenon began in the 1940s.  Yet despite decades of evidence, and the fact that opinion polls (such as Gallup) have consistently shown that the majority of people believe that flying saucers are real, this phenomenon has yet to be seriously and systematically investigated by the academic and scientific mainstream. Why? In large part, it has to do with the hypothesis that unexplained UFO sightings represent encounters with artificial, intelligently-controlled craft of non-terrestrial origin. Extraordinary evidence, such as an alien body or an intact craft, has yet to be made publicly available; many claim that such evidence is indispensable to justify any serious investigation at all into this issue, as claims that Earth has been visited by a non-terrestrial intelligence are inherently extraordinary. But while perhaps intuitively correct, this notion crumbles in the face of logical reasoning and facts.