The purpose of this brief thesis is to examine the concept of the group mind, in order to determine its validity. And, in the light of the analysis made, to attempt a decision as to whether or no it is a useful concept. To a large extent an inquiry of this nature is essentially historical. The various theories embodying the concept, which have been held by numerous thinkers, must be examined in turn. Such an inquiry is not of merely theoretical significance. If the notion of the group mind be proved valid, it must largely determine the whole orientation of the social sciences, of economics, of history, of politics, of sociology and social psychology. All these sciences are intimately related to the everyday life of the social animal, man. The question is probably more vital today than ever in the past, for never has a true interpretation of the facts of national life and of social life in general ben more urgent. During the last few years, in several quarters of the civilized world, political creeds and practices have come into force which make an inquiry such as it is proposed to undertake here, a matter of outstanding interest and importance.