During the last few years I have had the privilege of working with several historians who have offered me the opportunity to see their laboratory and to examine the product of their work long before it is ready for publication. The discussions that these collaborative efforts generate go well beyond a simple exchange of ideas between a psychoanalyst and a historian. They seem to produce an intense affective response, the presence of which indicates the strength of the psychological forces operating behind the ideas exchanged. This experience has directed my attention to the process of historical investigations, and I have attempted to study it in a more systematic way and to integrate it with the basic method and principles of psychoanalysis. The historian's work is long and laborious. It involves extensive study of many years' duration. He develops his ideas gradually and formulates his findings many times before he produces his final product. This involved process generates powerful psychological reactions that grossly affect his life in general and change his perception of himself and