The contributors to this monograph were selected from among those writers who had written on the psychology of thinking most recently, and the scope of the publication was determined by the aspects and problems presented by them. Naturally, it was not possible to include all whom we might have wished to include, or to present completely the present status of the psychology of thinking. Geographical location made it impossible for certain persons from abroad to participate, and personal and social factors prevented certain psychologists in the United States from accepting our invitation. In spite of these limitations, the contents of this publication demonstrate that we have been able to present what appear to be the major problems occupying present-day psychologists in the field of the psychology of the thought process. Although there may be some workers who will not find in our presentations problems with which they are most occupied, the essential problems recently dealt with in the United States are offered. It should be noted that we have consciously avoided adherence to the scope of any specific school of psychology; we have tried to widen the scope to the degree deemed necessary to gain constructive aspects for further development.Anyone who has not limited his scientific endeavors to the advancement of some personal scientific interest or to the scheme of thought of a specific school and who is willing to give a wider horizon to his science must attempt to find a stand from which he can obtain a bird's-eye view of the basic trends and problems of the field and its tasks. One of the most valuable stands for gaining such a widened view of an aspect of science is the historical one. This is especially true with regard to our subject, the psychology of thinking, which has undergone rather unfortunate treatment by leading groups during the most recent period of developments in the field.In turning back to the history of psychology, I fear we must cause some displeasure to the followers of J.B. Watson by going back to Descartes, whom Watson ridiculed because he misunderstood the basic Cartesian thesis. Cogito ergo sum was actually not "designed to save the human soul from the church fathers" (Watson, 1928), but to give modern man in his cogito experience (that is, in his thinking) an element of certainty that went far beyond any religious belief. Out of the multiplicity of human perception and experience, thinking was singled out as the surest and most objective element in human existence for bringing man to reality and truth. This, and this predominantly, makes thinking such an important factor in the human psyche, and it is the establishing of the importance of this factor that is the essence of Cartesian philosophy and psychology.