The Neo-Confucian philosopher Cheng Yi 程頤 (1033-1107) is most famous for his renewed understanding of the Confucian tradition. In particular, his thinking puts much emphasis on the notion of li 理 ("principle", "order", "coherence"). He thus in-fluenced many later Neo-Confucian thinkers, f.ex. Zhu Xi 朱熹 (1130-1200). Now it has often been argued that Cheng's thinking needs to be understood against the back-drop of Buddhism, esp. the Huayan school. This M.A. dissertation aims at sheding new light on the intricate relation between Neo-Confucian thinking and Buddhism. The first chapter introduces the basic question and reviews the research literature. In the second chapter, the author gives an overview of Buddhism in the Northern Song dynasty. The third chapter explores how Cheng Yi attempted to clarify his thinking against the backdrop of Buddhist thinking. The fourth chapter aims at discussing the relationship between Cheng Yi's Neo-Confucian vision and Buddhism by means of three aspects, namely ontological theory, theory of human nature, and practical dis-course. Finally, the fifth chapter presents a number of concluding remarks and discusses further philosophical implications. This dissertation focuses primarily on Cheng Yi's remarks in the Collected Writings of the Two Cheng and, secondarily, to Cheng Yi's commentary to the Book of Changes.