What is the nature of unidentified aerial phenomena? Forty years ago a small cadre of dedicated researchers began actively investigating cases, interviewing witnesses, and exchanging data through a small, informal network of international contacts. Today this low-profile network, or invisible college, has grown into a larger, multi-nation volunteer research effort joined by many individuals. But the questions first raised forty years ago remain current--and unanswered. I believe that a powerful force has influenced the human race in the past and is again influencing it now. Does this force represent alien intervention, or does it originate entirely within human consciousness? This is the question that forms the basis of the work of the Invisible College of UFO researchers.--Jacques Vallee