The mystery of UFOs has puzzled people for years. Have we really been visited by aliens from outer space? If so, why don't we have more evidence? Can we get to the bottom of this mystery using science and logic, or will it continue to mystify us forever? Discover all of the theories, from the reasonable to the ridiculous, then decide for yourself what to believe. Learn how scientists analyze and explain fakes and hoaxes. This book includes eyewitness accounts, dramatic photographs, up-to-date information, a glossary, further resources, and web search tips.