This article deals with development of basic management structures of large American corporations. In general, the problem has been one of growing operational complexity; the solution commonly adopted has been operational decentralization. This solution, however, has raised difficult questions of control, and various administrative answers have been evolved. These have fallen into recognizable patterns, for an examination of case histories graphically illustrates the close connection between the nature of a company's business and its administrative structure. Those firms whose activities cross established industry lines have tended toward product decentralization. Companies producing a relatively restricted line have decentralized on a functional or a geographic basis. Market-oriented firms have tended to decentralize on a geographic basis. Among the fifty companies studied, however, other variations are discernible. Historical analysis of the decentralization trend also suggests the importance of management personalities in governing the timing of structural changes and indicates clearly the reasons why some companies have yet to find decentralization a meaningful answer for their prevailing administrative problems.