What Is Web 2.0?

Web 2.0 is a conceptual label for the second generation of World Wide Web practices and technologies, characterized by dynamic, user-generated content, social interaction, and interoperability across web-based services, in contrast to the largely static, read-only pages typical of the web's first decade. The term was popularized at the 2004 Web 2.0 Conference co-organized by Tim O'Reilly and MediaLive, where O'Reilly articulated the "web as platform" thesis: that the web had shifted from a medium for delivering documents to a computing infrastructure in which user participation itself generates value. The O'Reilly Media essay "What Is Web 2.0" from 2005 remains the canonical formulation of this shift, describing principles such as harnessing collective intelligence and treating software as a service rather than a packaged product.

Web 2.0 is not a formal technical standard but a cluster of design principles and enabling technologies: Ajax (Asynchronous JavaScript and XML), RESTful APIs, RSS and Atom feeds, and server-side scripting frameworks that together made web applications behave more like desktop software while remaining accessible through standard browsers.

User-Generated Content and Social Platforms

The defining social feature of Web 2.0 is the inversion of the content creation model. Under Web 1.0 practices, a small number of publishers created content consumed by many users. Web 2.0 platforms are architecturally designed to aggregate the contributions of their users. Blogs, wikis, social bookmarking, and video-sharing sites emerged as dominant forms early in the transition; by the late 2000s, social networking services such as Facebook, Twitter, and LinkedIn had become the primary expressions of the model at scale. Recommendation and ranking algorithms depend on signals such as likes, shares, comments, and ratings, making the crowd itself the editorial mechanism. This architecture introduced challenges including misinformation propagation, privacy exposure, and platform concentration that continue to be studied in information systems research.

Rich Internet Applications and APIs

On the technical side, Web 2.0 applications adopted asynchronous communication between client and server, allowing web pages to update individual components without reloading the full document. The Ajax pattern, in which JavaScript calls XMLHttpRequest to fetch data in the background, became the standard mechanism for implementing this behavior. Web application frameworks, mashups that combined data from multiple public APIs, and the SaaS (Software as a Service) delivery model all accelerated during this period. Open web APIs allowed third-party developers to build services on top of existing platforms, a practice that shifted significant software value creation to the ecosystem rather than the platform alone. Standards bodies including the W3C worked on the XMLHttpRequest specification that formalized the mechanism underpinning Ajax interactions.

Participatory Architectures and the Read-Write Web

Web 2.0 architecture is built around systems that record, aggregate, and re-surface user activity. Collaborative filtering, the technique used by recommendation engines to infer preferences from the behavior of similar users, became commercially central during this era. Tagging and folksonomy, in which users assign free-form labels to content, represented a crowd-sourced alternative to hierarchical, editor-assigned classification systems. These participatory structures drove the rapid growth of open-source communities and knowledge aggregation projects. Research published in ACM Communications on collaborative systems examined the governance and quality dynamics of large-scale peer-produced content.

Applications

Web 2.0 has applications in a wide range of fields, including:

• Social networking and professional community platforms
• E-commerce reviews, ratings, and peer recommendations
• Online education and collaborative learning environments
• Crowdsourced mapping and geographic information services
• Open-source software development and version control hosting
• Enterprise knowledge management through wikis and intranets