Every day, we make decisions about what to share and when, how much to expose and to whom. Securing the boundary between one’s private affairs and public identity has become an urgent task of modern life. How did privacy come to loom so large in public consciousness? Sarah Igo tracks the quest for privacy from the invention of the telegraph onward, revealing enduring debates over how Americans would―and should―be known. The Known Citizen is a penetrating historical investigation with powerful lessons for our own times, when corporations, government agencies, and data miners are tracking our every move.