For many years, people have been interested in the origin of dreams. In his book, M. Jouvet tells how dreams are born, what relationship exists between sleep and wakefulness, and how it led him to the discovery of “paradoxical sleep” - a condition in which the brain exhibits extreme activity. It is at this moment that our consciousness works very clearly. To understand it, the author turns to the experience of philosophers - among them Locke, Hegel, Kant, Hume, Husserl, and speaking about the subconscious, he recalls Freud. In conclusion, M. Jouvet describes new research aimed at studying the capabilities of the brain - the main secret of man, which No one has yet managed to solve it.