This is a book about unidentified flying objects-UFO's-"flying saucers." It is actually more than a book; it is a report because it is the first time that anyone, either military or civilian, has brought together in one document all the facts about this fascinating subject. With the exception of the style, this report is written exactly the way I would have written it had I been officially asked to do so while I was chief of the Air Force's project for investigating UFO reports-Project Blue Book.