The main purpose of this article is to serve as an introduction to the foregoing translation of Mao Tse-tung's essay, “The Great Union of the Popular Masses,” written during the summer of 1919. As suggested by the title, however, while focusing primarily on Mao Tse-tung's thought at the time of the May Fourth Movement, I have chosen to develop also certain parallels with the ideas he has put forward more recently, especially during the Cultural Revolution. That there are elements of continuity between these two epochs has been recognized by everyone from the very beginning of the Cultural Revolution. Indeed, Mao himself not only stressed these links, but, for a time at least, sought to exaggerate them. The Cultural Revolution was (among many other things) an attempt to re-create, for the benefit of today's youth, an experience analogous to that of Mao's generation of young Chinese half a century ago. None the less, the juxtaposition, for purposes of analysis, of two such episodes widely separated in time may at first glance appear somewhat arbitrary. Such an approach can, in my view, be justified by the fact that the Mao Tse-tung of 1919 had not yet seriously begun to assimilate Marxism, whereas the Mao Tse-tung of the Cultural Revolution had already moved beyond Marxism to conceptions not altogether compatible with the logic of Marxism or of Leninism. The intervening years, during which he mastered, applied and then to some extent discarded the principles of revolution developed by Lenin and Stalin are, of course, vitally important to an understanding of the genesis and present significance of his thought. But by looking directly from 1919 to 1969, and leaping over the intervening period, one can perhaps see the problem in a perspective which reveals points that would otherwise be obscured. In particular, one can note the persistence of traits and ideas not derived from Marxism, and which therefore belong to an earlier and deeper stratum of Mao's thinking and feeling about the problems of Chinese society.