The purpose of this study is to show that within the context of Nigeria's development effort, financial development with respect to the banking system has aided investment and economic development to a greater extent than is generally recognised. This study, therefore, sets itself the task of a detailed examination of the structure of the Nigerian banking system as a service producing industry, the analysis of the economic performance of the banking system arid the prescribing of policies and regulations to improve the banking system's structure and performance. The structure of the Nigerian banking system is reflected in its historical pattern of growth, ownership, the network branch expansion, assets and liabilities composition and the legal and regulatory framework. The economic performance is reflected in output, profitability and the efficiency with which the banks have met some requirements indeispensable for economic development such as the contribution to saving-investment process and the provision of adequate finance to various sectors of the economy. A banking system, as a service industry, suffers from output measurement problem. Surrogates were used to measure the output of the Nigerian banking systems. The profitability of the banking system was measured by the ratios of profit after tax/capital and profit after tax/assets. The determinants of the Nigerian banking system's lending and profitability performance are based on the hypothesis: the demand, policy and structure variables significantly affect the performance of the Nigerian banking system. The evidence from the analysis indicates xii that policy and demand factors were more important in influencing the performance of the banking system. The bank market structure as measured by the bank offices rather than the deposits concentration ratio was significant in influencing the Nigerian banking system's performance. The study i rounded up by prescribing policies and regulations to improve the structure and performance of the Nigerian banking system.