Do ghosts exist? Do you believe in ghosts? Many thousands of people claim to have seen them, even interacted with them - and often even entrenched sceptics have been converted by a moment's brush with 'impossible' paranormal entities. Sometimes ghosts are benign, protecting and warning about imminent danger; sometimes they are neutral, merely appearing and disappearing without any apparent awareness of the living. But sometimes they are evil, causing untold mental and physical problems for those they haunt - especially the destructive hauntings known as poltergeists.