In an age of information overload, it is easy to fall back on our own prejudices and insulate ourselves with comforting opinions that reaffirm our core beliefs. Crowds quickly become mobs. The justification for the Iraq war, the collapse of Enron, the explosion of the space shuttle Columbia--all of these resulted from decisions made by leaders and groups trapped in "information cocoons," shielded from information at odds with their preconceptions. How can leaders and ordinary people challenge insular decision making and gain access to the sum of human knowledge?

Stunning new ways to share and aggregate information, many Internet-based, are helping companies, schools, governments, and individuals not only to acquire, but also to create, ever-growing bodies of accurate knowledge. Through a ceaseless flurry of self-correcting exchanges, wikis, covering everything from politics and business plans to sports and science fiction subcultures, amass--and refine--information. Open-source software enables large numbers of people to participate in technological development. Prediction markets aggregate information in a way that allows companies, ranging from computer manufacturers to Hollywood studios, to make better decisions about product launches and office openings. Sunstein shows how people can assimilate aggregated information without succumbing to the dangers of the herd mentality--and when and why the new aggregation techniques are so astoundingly accurate.

In a world where opinion and anecdote increasingly compete on equal footing with hard evidence, the on-line effort of many minds coming together might well provide the best path to infotopia.