Historians traffic in timekeeping, and time is the fundamental building block of historical scholarship, whether we are telling stories about change, persistence, sequence, or simultaneity. So in a way, books like this, which study how earlier societies experienced the time units that historians depend upon to make sense of the past, are contributions to the basic science of our discipline. In my own scholarship on nineteenth-century America, however, a study of the week fits a more particular pattern. I have always been drawn to the history of unspectacular technologies that have contributed in subtle ways to the modern experience of connectedness. Rather than looking at the impact of steam railroads, combustion engines, electromagnetic telegraphy, faster printing presses, innovative techniques of photography and film, or other celebrated inventions, I have made a career of studying much older methods of communication and social organization (written signs, printed newspapers, postal relays) that have been used in novel ways, typically without fanfare, to create broad, impersonal networks of connection among masses of people. These networks are typically forms of invisible social infrastructure, whose users occasionally commented upon their power or novelty but which we mostly now take for granted. I became curious about the history of the week for similar reasons. More than just a religious observance or calendar of rest days, the modern seven-day week is a form of social infrastructure. It incorporates the habits, routines, and rhythms of people we don’t see and might not even know, and it weaves those habits, routines, and rhythms into the fabric of time as we perceive it.