The thesis analyses the economics, concept, and design of information intermediaries. Information intermediaries are independent, trustworthy information processing third parties who mediate information between information sources and information seekers in order to overcome problems of information overload and the uncertainty about the quality of information. The analysis develops an economic model based on the microeconomic theory of search and applies it to information intermediaries who provide services like the search for information or the mediation of information. Examples of these information intermediaries can be found in multiple forms on the Internet. The model identifies the basic influencing factors of the intermediary’s environment, investigates the impact of these environmental conditions on the information intermediary, and derives the optimal strategy of the information intermediary under different environmental circumstances.