Using a term coined by the contemporary Chinese philosopher Mou Zongsan, we could define Zhou Dunyi's thought in terms of ‘moral metaphysics’. Zhou Dunyi, a thinker who lived in Northern Song period, developed a philosophy that shows an ontological link between the cosmic order of the universe and the human moral reality. His contribution consists of two short works, Penetrating the Book of Changes and Discussion of the Supreme Polarity Diagram. These works played a fundamental role in creating the metaphysical (...) structure of the neo-Confucian thought: Zhu Xi emphasized Zhou Dunyi's contribution to the neo-Confucian philosophy and, more precisely, he pointed out how Zhou Dunyi's ideas helped to define the conceptual framework of neo-Confucianism. Moreover, Zhu Xi legitimized Zhou Dunyi's role as the pioneer of the ‘Learning of the Way’, or the renewed neo-Confucian tradition. This paper aims to provide an overview of Zhou Dunyi's crucial role in the field of neo-Confucianism. At the same time, we stress the need for further analysis in order to fully understand the value of Zhou Dunyi's philosophy in the Song period intellectual context. (shrink)