This is a book about how we experience and imagine time. Although treatments of that subject often focus on the clock, modern time consciousness is organized around calendars as well. The Week considers one of the most powerful calendrical rhythms in our lives. Seven-day cycles are ancient timekeeping devices, but they are completely conventional and until the last century many parts of the world functioned smoothly without them. Only in the modern era have seven-day rhythms become the dominant beat in our lives, so much so that not knowing the day of the week presents as a singular symptom and symbol of disorientation. Other inquiries into weekly timekeeping have observed its artificial character, but this book explores the modern week as the product of historical changes. How did we come to be so attached to our weeks? Part of the answer has to do with industrial labor arrangements, which use the traditional seven-day Sabbath cycle to regulate the relationship between work and leisure. The modern week, however, is not simply an alternation between weekdays and weekends. If it were, then we would probably be less viscerally attached to the different feel of Tuesdays and Wednesdays, for example. Those days have distinctive characters, not simply because of their relative positions in the work cycle (or the cycle of Sabbath observance), but because so many of us have different routines and schedules on different days of the week.My account of the week in the United States argues that a crucial historical development entrenched weekly calendars in the mental time-maps of ordinary Americans. Starting in the early nineteenth century, masses of people in the United States, especially those living in towns and cities, attending school, earning wages, performing housework, going to the theater, joining lodges, reading newspapers, receiving mail, or doing numerous other things that relied on the technology of the week to coordinate the activities of strangers, suddenly had new reasons for caring where they stood in the seven-day cycle.My book documents this historical development for those readers who might be curious (or skeptical) about how and when it happened, but it also traces how the new weekly consciousness shaped the way Americans remembered and accounted for events in their lives – in their diaries, memoirs, and personal correspondence, and even when called into court to testify. Because weeks became so linked to memory, their rhythms acquired a firmer grip on mass time consciousness. This in turn helps explain both why attempts to modify the weekly calendar have failed, and why in times (such as the recent pandemic shutdown) when we lose track of our weeks, the blurring of our Tuesdays and Wednesdays can make us feel more generally unmoored.