We take the seven-day week for granted, rarely asking what anchors it or what it does to us. Yet weeks are not dictated by the natural order. They are, in fact, an artificial construction of the modern world. With meticulous archival research that draws on a wide array of sources—including newspapers, restaurant menus, theater schedules, marriage records, school curricula, folklore, housekeeping guides, courtroom testimony, and diaries—David Henkin reveals how our current devotion to weekly rhythms emerged in the United States during the first half of the nineteenth century. Reconstructing how weekly patterns have insinuated themselves into the social practices and mental habits of Americans, Henkin argues that the week is more than just a regimen of rest days or breaks from work: it’s a dominant organizational principle of modern society. Ultimately, the seven-day week shapes our understanding and experience of time.