Sleep Walking and Moon Walking is a classic psychology essay that deals with the subject of sleep walking. Psychoanalysis holds a key to the problem of sleep walking, which alone has been able to unlock the mysteries of its causes and its significance. This key is the principle of wish fulfilment, an interpretative principle which explains the mechanisms of the psyche and illuminates the mental content which underlies these. Sleep walking as a method of wish fulfilment evidently lies close to the dream life, which has become known through psychoanalysis.