We present an OLG endogenous growth model in which a reduction in the level of concentration in the banking industry exterts two opposite e.ects on economic growth. On the one hand, it induces economies of specialisation which enhances intermediation e.ciency and thereby eco- nomic growth. On the other hand, it results in duplication of fixed costs which is detrimental for e.ciency and growth. The trade o. between the two opposing e.ects is ambiguous and can vary along with the dynamic process of financial and economic development. Using cross country in- dustry data we find that banking concentration is negatively associated with industrial growth only in low income countries while there is no such asssociation in high income countries. These empirical findings support the model.s prediction that there exist a di.erent relationship between banking concentration and growth depending on the level of economic development.