To date, the firm conclusions of Project Blue Book are: 1. no unidentified flying object reported, investigated and evaluated by the Air Force has ever given any indication of threat to our national security; 2. there has been no evidence submitted to or discovered by the Air Force that sightings categorized as UNIDENTIFIED represent technological developments or principles beyond the range of present-day scientific knowledge; and 3. there has been no evidence indicating that sightings categorized as UNIDENTIFIED are extraterrestrial vehicles. - the summary of Project Blue Book, an Air Force study of UFOs from 1950 to 1965, as quoted by James Randi in Flim-Flam!