Americans spend billions of dollars every year on drugs, therapy, and other remedies trying to get a good night’s sleep. Anxieties about not getting enough sleep and the impact of sleeplessness on productivity, health, and happiness pervade medical opinion, the workplace, and popular culture. In The Slumbering Masses, Matthew J. Wolf-Meyer addresses the phenomenon of sleep and sleeplessness in the United States, tracing the influence of medicine and industrial capitalism on the sleeping habits of Americans from the nineteenth century to the present. Before the introduction of factory shift work, Americans enjoyed a range of sleeping practices, most commonly two nightly periods of rest supplemented by daytime naps. The new sleeping regimen—eight uninterrupted hours of sleep at night—led to the pathologization of other ways of sleeping. Arguing that the current model of sleep is rooted not in biology but in industrial capitalism’s relentless need for productivity, The Slumbering Masses examines so-called Z-drugs that promote sleep, the use of both legal and illicit stimulants to combat sleepiness, and the contemporary politics of time. Wolf-Meyer concludes by exploring the extremes of sleep, from cases of perpetual sleeplessness and the use of the sleepwalking defense in criminal courts to military experiments with ultra-short periods of sleep. Drawing on untapped archival sources and long-term ethnographic research with people who both experience and treat sleep abnormalities, Wolf-Meyer analyzes and sharply critiques how sleep and its supposed disorders are understood and treated. By recognizing the variety and limits of sleep, he contends, we can establish more flexible expectations about sleep and, ultimately, subvert the damage of sleep pathology and industrial control on our lives.