The primary purpose of this study is to develop a framework that will explain the behavior of financial intermediaries and, more precisely, their pricing policies. As financial intermediation is the business of financial assets and liabilities, use is made of concepts and models developed tradition­ ally in Finance and Economics to end up with recommendations not only for optimal choices of interest rates but also for proper regulation and more sensible accounting methods. Also, the econometric implications of deposit rates stickiness are examined and empirically tested on Belgian data. My debt to many people has been growing during these years and it is a great pleasure to print a text and have the opportunity to thank those who have been so helpful. First of all, let me thank Professor Jacques Dreze, my thesis director. I am grateful to Jacques for encouragments, guidance and so many stimulating discussions. I also thank the members of the Jury, Professors A. Jacquemin, A. Kervyn de Lettenhove, A. Lamfalussy, P. Reding and A. Siaens for comments on earlier drafts of the manuscript. Discussions with Professor P. Howitt while he was visiting the Center for Operations Research and Econometrics (C.O.R.E., Universite Catholique de Louvain) in 1979 have greatly contributed to my understanding of the economics of risk sharing between lenders and borrowers. Philippe Gille has been extremely helpful in carrying out the joint econometric estimation in Chapter Five and in suggesting a fine way to present the results.