The Web as we know it is being threatened in different ways. Some of its most successful inhabitants have begun to chip away at its principles. Large social-networking sites are walling off information posted by their users from the rest of the Web. Wireless Internet providers are being tempted to slow traffic to sites with which they have not made deals. Governments—totalitarian and democratic alike—are monitoring people’s online habits, endangering important human rights. If we, the Web’s users, allow these and other trends to proceed unchecked, the Web could be broken into fragmented islands.