The ghost experience is a remarkably common one. Ghosts are seen or heard, or the their presence is felt in almost every kind of place by almost every kind of person. They appear once, or regularly, with a purpose, or for no apparent reason. They may be friendly, hostile, or peculiar, and seen by one person or several. Most are recognisably human, but some are merely bright lights or animals or even objects, such as an aeroplane. Some take the form of poltergeists, vampires or zombies. Most are dead, but some are still alive, and a number of people have seen ghosts themselves. They are recorded from the earliest times down to the present, and each age has asked, 'Why ghosts?' and offered its own explanation.

P.G. Maxwell-Stuart's book traces the history of ghost phenomena through the ages and the ways in which people have tried to deal with the hope, the fear, the curiosity, and the disbelief which ghosts have aroused, and to the question, 'Why ghosts?', he poses another, 'Why not?'.