What happens to democracy and free speech if people use the Internet to listen and speak only to the like-minded? What is the benefit of the Internet's unlimited choices if citizens narrowly filter the information they receive? Cass Sunstein first asked these questions in 2001's Republic.com. Now, in Republic.com 2.0, Sunstein thoroughly rethinks the critical relationship between democracy and the Internet in a world where partisan Weblogs have emerged as a significant political force. Republic.com 2.0 highlights new research on how people are using the Internet, especially the blogosphere. Sunstein warns against "information cocoons" and "echo chambers," wherein people avoid the news and opinions that they don't want to hear. He also demonstrates the need to regulate the innumerable choices made possible by technology. His proposed remedies and reforms emphasize what consumers and producers can do to help avoid the perils, and realize the promise, of the Internet.