In 2001, the bursting of the dot-com bubble led some analysts to argue that the World Wide Web was overhyped. A few years later, in a brainstorming session to organize a conference in the fall of 2004, technology publisher Tim O'Reilly and web pioneer Dale Dougherty noted that the organizations and companies that survived the crash were more important than ever and that they shared similar business models, design, and development patterns. The term Web 2.0 was adopted to describe the emergent physiognomy of the web and to name the upcoming conference. The term Web 2.0 has been criticized as being a marketing buzzword and as promoting the idea of a technological revolution that did not happened, but O'Reilly and Dougherty's analysis behind the term was indeed about the market and the economy, and about a "natural selection" among existing models rather than a tabula rasa revolution. To clarify his thoughts, in 2005 O'Reilly published the seminal article "What is Web 2.0". This entry explores the characteristics drawn by O'Reilly of Web 2.0 phenomenon, how most of them succeeded in changing the way contents and software are produced , how a few others failed, and the societal implications of both of these success and failures. It then discusses if the Semantic Web, sometimes called "Web 3.0", can be considered as the successor of Web 2.0.