Sleep: for millennia, it has been the subject of myths, stories, and images. Humans spend a good third of their lives asleep. The time we spend sleeping is an unconscious, unproductive, and inactive period, but also a vital and longed-for time. How does a society, in which scientific understanding, rationality, and efficiency play a central role, deal with such a stubborn phenomenon as sleep? Hannah Ahlheim's study on the development of sleep knowledge in Germany and the USA since the late 19th century consistently connects the history of a science with the history of modern society. It shows that not only has the image of the sleeping body, the dreaming soul, or the dreaming brain changed. The work with perpetually awake machines and the blurred boundaries between day and night.