The classic UFO--shaped like a flying saucer with a dome on top--in reality represents but a small fraction of the mystery aerial objects people have reported seeing over the past half century or so. Eyewitnesses around the world actually describe a bewildering array of forms in flight. Here, for the first time, is a comprehensive look at the physical structure of UFOs, a book devoted to identifying and categorizing the dozens of different shapes the UFO phenomenon exhibits globally. From double-ringed to triangle-shaped UFOs, from saucers to cigarshaped craft--and more--this book documents each variant, describes often extraordinary encounters, and even takes the extra step of offering the skeptic's explanation for some of the sightings. What can the shape of a UFO tell us? In some cases, the shape of the object or phenomenon provides a strong clue to its origin. But in all cases, the classification system developed in this book shows quite clearly that there is no single solution to the UFO mystery--there are most likely many answers. And some surprises too.