Intermediaries are software programs or agents that meaningfully transform information as it flows from one computer to another. Many contemporary web services are intermediaries, performing functions of transforming new feeds and airline reservation databases into categorized and personalized web pages. The article discusses the role executed by intermediaries to personalize information streams. It presents the design, development and deployment of intermediary-based web processing. Many current web services are based on intermediary processing models. A news portal acts as an intermediary by deciding how to present stories to the user. For example, Yahoo! News puts three top headlines on its first page, and produces separate pages for each category. Intermediaries work in several ways, performing implementation issues, intermediary functions, customizing, filtering, annotating, transcoding aggregating and caching information. The notion of intermediaries can be generalized to incorporate processes that produce personalized information, and much more. INSET: URLs for Further Information