Web 2.0 may be an elusive concept, but one thing is certain: using the Web as merely a means of retrieving and displaying information is history. Today s Web is immediate, interactive, innovative. It is user-controlled and community-driven. Organizations, marketers, application developers, and communicators must be ready to respond and to innovate or be left behind, and the experts featured on these pages are leading the charge. Their ideas are fresh, sometimes experimental, necessarily flexible, and always on the leading edge to prepare you for a Web where users rule.