1 Introduction.- 1.1 Information overload.- 1.2 The aim and procedure of the analysis.- 1.3 The organization of this thesis.- 2 Information.

- 2.1 Basic aspects of information.- 2.2 Sources of information.- 2.3 The credibility of information and trust in the information source.- 2.4 Information and market efficiency.

- 2.5 Information as an economic commodity.- 3 Intermediation.- 3.1 Basic concepts and functions of intermediaries.- 3.2 Justification of intermediaries.- 3.

3 Intermediary contracts and sources of income.- 3.4 Effects of intermediation on markets.- 3.5 Market microstructure.- 4 An economic model of information intermediaries.- 4.1 Introduction.

- 4.2 The economic theory of search.- 4.3 Model of an information intermediary.- 4.4 The influence of environmental conditions on the intermediary's strategy.- 4.5 Competition between information intermediaries.

- 4.6 Welfare effects through the information intermediary.- 4.7 Extensions to the basic intermediary model.- 4.8 Summary.- 5 Concepts and design of information intermediaries.- 5.

1 Information intermediaries.- 5.2 Network-based intermediaries.- 5.3 Network-based information intermediaries.- 5.4 Summary: economic aspects of network-based information intermediaries.- 6 Conclusion.

- 6.1 Summary.- 6.2 Outlook: the future of network-based intermediaries?.- 7 References.- 8 Appendix.- 8.1 Appendix A: development of the number of Internet hosts.

- 8.2 Appendix B: simplification of (eq. 9) using integration by parts.- 8.3 Appendix C: transformation of (eq. 12) into (eq. 13).- 8.

4 Appendix D: proof of the indifference property.- 8.5 Appendix E: number of solutions of the system of equations in the broker model.- 8.6 Appendix F: partial derivatives of intermediary's profit.- 8.7 Appendix G: list of examples and URLs.-List of figures.

- List of tables.- List of used symbols.- List of abbreviations.