Randles and Warrington establish by detailed case histories of many UFO sightings that unexplained phenomena certainly exist. Picking their way expertly through the maze of misinformation and fantasy, they examine the possible explanations, rejecting the 'standard' view- that UFO's are alien spaceships- in favour of more scientifically based and testable ideas. They suggest ways in which scientific standard should be applied and consider the fruits that such enquiries might yield- and the potential consequences for mankind of explaining the hitherto inexplicable.