Both revenues and earnings of diversified firms are increasingly being reported, to the government and the public, on a subentity basis. Adequate criterial foundations do not exist to permit the effective general prescription of specific segment delineations, nor is it known whether such criterial assists can be usefully developed.Demands for segmentation in financial reports are currently intense. Actual reporting practices are largely nonstandardized as to either the definition of segments employed or, the disclosure modes used to present them. Neither conceptual nor theoretical supports are now adequate in guidance to the forms and levels of segmentation activity now required. Prerequisite to effective development of such supports is an-adequate understanding of the corporate diversification phenomenon itself. This dissertation project investigates and analyzes the nature of corporate diversification, as manifested in (1) its historical evolution; (2) general comprehensions of the phenomenon, as evidenced in published opinions and conceptual reasoning schemes of both authoritative experts and lay investors; and (3) formal research by others. Additionally, the results of these investigations and analyses are developed into conceptual schemes and theoretical frameworks, at moderate levels of abstraction.