Discusses phases of the sleep cycle, experimental work on sleep and wakefulness, sleep disorders and their treatment, and such sleep-like states as hypnosis and hibernation.

Aserinsky, one of Kleitman's graduate students, decided to hook sleepers up to an early version of an electroencephalogram machine, which scribbled across ¹⁄₂ mile (800 m) of paper each night. In the process, Aserinsky noticed that sleepers went through periods when their eyes darted wildly back and forth several times each night. Kleitman and Aserinsky introduced the world to "rapid-eye movement," or REM sleep, and demonstrated that REM sleep was correlated with dreaming and brain activity. 

The authors conducted the first intensive study of the relationship between rapid eye movement (REM) sleep and dreaming.