In this article, the author examines the work of the Neo-Confucian thinker Zhou Dunyi (1017-73), particularly his seminal essay, "Explanation of the Diagram of the Great Ultimate" (Tajitu shuo), as a key articulation of the anthropocosmic vision that underlies the traditional Chinese practice of taijiquan. Although often associated with Daoism, the art of taiji actually draws on cosmological principles widely shared by followers of all Chinese schools of thought. Through a careful reading of Zhou's essay, it becomes apparent that Zhou is deeply versed in this very ancient pan-Chinese cosmic vision, giving his essay a decidedly mystical air. However, Zhou also takes pains to give his essay a distinctive Confucian flavor by stressing the necessity of human moral action in establishing proper cosmic balance. This marriage of the more mystical (Daoist) and practical/ moral (Confucian) suggests that Zhou himself may have been a practitioner of some form of taijiquan, as that are functions by combining both aspects of Chinese philosophy. Whether this suggestion is true or not, however, Zhou's "Explanation" stands as perhaps the best articulation of the "essence" of taiji found in traditional sources.