Believers in flying saucers tend to ignore the 98 per cent of cases fully explained by the Air Force, and to focus attention on the 2 per cent that remain puzzling. Yet no distinguishable difference exists between the types of observation described in solved and in unsolved cases. From considering the original reports, the competence of the witnesses, and the appearance and movements of the various UFOs, no analyst could predict in advance which will be fully accounted for and which will not. The witnesses (often technically trained observers or experienced airmen) in the cases that are solved are just as reliable as--and no less so than--the witnesses in the unexplained cases. They report the same classes of phenomena--glowing UFOs, hovering UFOs, UFOs moving at high velocities, making incredible maneuvers, and behaving as though under intelligent control. The Air Force has accounted for nearly all of these flying saucers. The various causes included aircraft, balloons, satellites, mirages, inversions, hoaxes, delusions, reflections, birds, lenticular clouds, ball lightning, radar anomalies, sundogs, meteors, planets, stars, the Aurora, and other astronomical phenomena. The few remaining cases report similar observations and undoubtedly have one of these causes--which cannot be proved because some essential fact is missing. No data in these unsolved cases suggest that the UFOs had an interplanetary origin or that they constituted a threat to the security of the United States. When Air Force investigators have determined that a UFO report does not represent anything of interest to Intelligence, their primary duty ends. However, since many UFO puzzles are of interest for scientific or technical reasons, the investigators try to find the specific explanation of each case and, if it has attracted public attention, give the final solution to the press. _Civilian Saucer Groups_