As the Internet grows more sophisticated, it is creating new threats to democracy. Social media companies such as Facebook can sort us ever more efficiently into groups of the like-minded, creating echo chambers that amplify our views. It's no accident that on some occasions, people of different political views cannot even understand each other. It's also no surprise that terrorist groups have been able to exploit social media to deadly effect. Welcome to the age of #Republic. In this revealing book, Cass Sunstein, the New York Times bestselling author of Nudge and The World According to Star Wars, shows how today's Internet is driving political fragmentation, polarization, and even extremism—and what can be done about it.