It would be interesting to present aggregate data on shifts in ownership of government bonds, corporate bonds, and listed stocks; on trends toward private placement; and on greater use of intermediate financial institutions. But, in deference to the numerous individual investors, large and small, trained and untrained, counseled and uncounseled, it would be difficult to draw valid conclusions. I propose to do something which is more fundamental, and perhaps more valuable to us in our profession, namely to trace the development of investment thought and apply the ideas to the many puzzling problems which investors are now facing. Obviously, it will be impossible to cover all literature in the field, so I shall limit myself to certain representative textbooks and monographs which have added appreciably to American investment thought, and which have influenced teachers and practitioners in the investment field. Undoubtedly, articles and pamphlets have greatly influenced all of us, but, of necessity, they cannot be included in a short review of investment thought. Since many of us have lived through much of the period under review, as students, teachers, investment bankers, investment counselors, investment managers, and investors, it is probable that our interpretations of the various contributions will not necessarily be in complete agreement.