BERLE AND MEANS [13] long ago noted the increasing diffusion of ownership in large American corporations and concluded that control was shifting from the stockholders to the managers. Since then, the Berle-Means (B-M) thesis has been the subject of continuous and heated controversy both within and without the profession, and has provided a major rationale for the introduction and expansion of government regulation of security transactions.' It is therefore astonishing that, almost forty years after the publication of The Modern Corporation and Private Property, the empirical evidence produced on either side of the issue has been negligible.2 Until recently, the B-M thesis rested entirely on faith and on data reflecting increased diffusion of share ownership, with no empirical evidence regarding the validity of the consequences alleged to follow from such diffusion. This failure to pursue more rigorous testing seems due, at least in part, to a misunderstanding of the meaning and role of private property in decision-making.' The purpose of this paper is to encourage the proper evaluation of the B-M thesis. Section I contains a brief discussion of the usefulness of data describing the distribution of shares among owners. Section II presents some theoretical issues relating to the B-M thesis, Section III considers the relationship between diffusion of ownership and private property, and Section IV examines the empirical evidence relating to the behavioral implications of the B-M thesis. Section V contains a few concluding remarks.