THE RAPID growth of the size of commercial banks during the last twenty years has emphasized the need for delegating responsibility and authority; this requires an effective organizational structure. The general objective of this research is to contribute to the understanding of bank organization toward the end of improving the efficiency of these institutions. The research consisted of detailed case studies covering ten midwestern banks ranging in size from $13,000,000 to $130,000,000 in deposits. The case studies were supplemented with personal interviews of over two hundred bank authorities, officers, and employees. The bank personality is a complex of several elements which, in interaction, give the bank a distinct individuality and partially determine the suitable organization structure. Size and other physical characteristics of the bank set certain requirements for the organization structure as conditioned by the history, traditions, and reputation of the bank. The nature of the market served by the bank determines the specific functions performed within the bank and provides the basis of departmentation. Finally, the human resources of the bank are an important consideration. These factors indicate that there is no one ideal organization structure suitable for all banks. The bank boards were found to function in four ways: they decide, confirm, counsel, and review. The research indicated that the informal relationships are often much more important than the formally defined functions. Important decisions are seldom made in the actual board meetings. The formal confirmation of management proposals was found to be unanimous by the board in practically all instances because of prior informal discussions between the board and top management. The chief executive is in a strategic position to influence the board of directors by selecting the problems brought before the board for action and the factual information supplied to the board.