The essay aims to analyze the concept and the paradigm of harmony in the metaphysical system of the Neo-Confucian philosopher Zhang Zai. It argues that Zhang Zai’s concept of Great Harmony not only inherits the traditional centrality of this idea within the Confucian tradition, but actually presents the most advanced idea of harmony up to his time. In Zhang Zai’s philosophy, harmony becomes the Way itself, which includes the realm of principles and the outward and functional manifestations of reality. This essay will deal with harmony in two ways: first with Zhang Zai’s direct use of the concept in the Zhengmeng and second, applying the paradigm of harmony to other of Zhang Zai’s key concepts such as qi 氣, void (xu 虛) and natural dispositions (xing 性).