Zhu Xi or Chu Hsi (朱熹, October 18, 1130, Yuxi, Fujian province, China － April 23, 1200, China) is a Song Dynasty(960-1279) Confucian scholar who became the leading figure of the School of Principle and the most influential rationalist Neo-Confucian in China. His contribution to Chinese philosophy includs his assigning special significance to the Analects of Confucius, the Mencius, the Great Learning, and the Doctrine of the Mean (the Four Books), his emphasis on the investigation of things (gewu), and the synthesis of all fundamental Confucian concepts.

During the Song Dynasty, Zhu Xi's teachings were considered to be unorthodox. Rather than focusing on the Book of Changes like other Neo-Confucians, he chose to emphasize the Four Books: the Great Learning, the Doctrine of the Mean, the Analects of Confucius, and the Mencius as the core curriculum for aspiring scholar officials. For all these classics he wrote extensive commentaries that were not widely recognized in his time; however, they later became accepted as their standard commentaries. The Four Books served as the basis of civil service examinations all the way down to 1905.

From 1313 to 1905, Zhu Xi's commentaries on the Four Books formed the basis of civil service examinations in China. His teachings were to dominate Neo-Confucians such as Wang Fuzhi, though dissenters would later emerge such as Wang Yangming and the School of Mind two and a half centuries later.

His philosophy survived the Intellectual Revolution of 1917, and later Feng Youlan would interpret his conception of li, qi, and taiji into a new metaphysical theory.