The writer relates the very powerful and well documented theatrical superstition that Shakespeare's Macbeth is the unlucky play. He suggests that this is not an historical accident but represents a hidden meaning in the play which can be revealed by a psychoanalytic reading: namely that the Macbeth-Lady Macbeth union is symbolically an incestuous relationship. The play is analysed according to this reading and evidence adduced in support of this hypothesis. This interpretation is shown to be tenable and to explain the attributes which attach to the play.