The World Wide Web can be considered a huge library that in consequence needs a capable librarian responsible for the classification and retrieval of documents as well as the mediation between library resources and users. Based on this idea, the concept of the “Librarian of the Web” is introduced which comprises novel, librarian-inspired methods and technical solutions to decentrally search for text documents in the web using peer-to-peer technology. The concept’s implementation in the form of an interactive peer-to-peer client, called “WebEngine”, is elaborated on in detail. This software extends and interconnects common web servers creating a fully integrated, decentralised and self-organising web search system on top of the existing web structure. Thus, the web is turned into its own powerful search engine without the need for any central authority. This book is intended for researchers and practitioners having a solid background in the fields of Information Retrievaland Web Mining.