Preface and acknowledgements; Introduction; Part I. Market Microstructure and the Intermediation Theory of the Firm: 1. Market microstructure and intermediation; 2. Price setting and intermediation by firms 3. Competition Part II. Competition and Market Equilibrium: 3. Competition between intermediaries; 4. Intermediation and general equilibrium; Part III. Intermediation Versus Decentralized Trade: 5. Matching and intermediation by firms; 6. Search and intermediation by firms; Part IV. Intermediation under Asymmetric Information: 7. Adverse selection in product markets; 8. Adverse selection in financial markets; Part V. Intermediation and Transaction Costs: 9. Transaction costs and the contractual theory for the firm; 10. Transaction costs and the intermediation theory of the firm; Part VI. Intermediation and Agency: 11. Agency and the organizational-incentive theory of the firm; 12. Agency and the intermediation theory of the firm; Conclusion.