The thesis consists of two parts. Part I investigates the interactive nature of the relationship between financial intermediation and economic growth. The main theoretical results are: a) financial intermediaries emerging as a consequence of agents' maximising behaviour at some critical level of economic development could have a negative impact on economic growth; b) the growth impact of financial institutions, i.e. financial intermediaries and stock markets, changes positively along the process of economic development; c) excessive financial intermediation might occur as a consequence of economic development; d) the co-evolution of credit markets, where financial intermediaries operate, and stock markets does not imply complementariness between the two elements of the financial sector; e) the emergence of a stock market might have an immediate detrimental effect on growth; f) the growth impact of the overall financial sector depends crucially upon the complementarity/substitutability relationship between stock markets and credit markets as sources of external finance. Part II, consists of two models which can be thought of as extensions of the material presented in Part 1. In the first, the impact of financial deepening in the context of a growth model where growth is driven by human capital accumulation is analysed. The result of this model is that, since financial transactions and training are substitutes as devices for intertemporal substitution of consumption, the availability of a technology for financial transactions might induce a negative growth effect. The second model deals with interregional trade in financial services. The outcome of this model is that, because of asymmetries in the incentives to trade in deposits and loans, free trade might have detrimental consequences for the regions whose financial sector is less efficient since local investment can be crowded out. The thesis establishes those propositions by theoretical reasoning and appropriate formal proofs.