Yuen Ren Chao (Chinese: 趙元任; 3 November 1892 – 25 February 1982), also known as Zhao Yuanren, was a Chinese-American linguist, educator, scholar, poet, and composer, who contributed to the modern study of Chinese phonology and grammar. Chao was born and raised in China, then attended university in the United States, where he earned degrees from Cornell University and Harvard University. A naturally gifted polyglot and linguist, his Mandarin Primer was one of the most widely used Mandarin Chinese textbooks in the 20th century. He invented the Gwoyeu Romatzyh romanization scheme, which, unlike pinyin and other romanization systems, transcribes Mandarin Chinese pronunciation without diacritics or numbers to indicate tones.

Chao was born in Tianjin in 1892, though his family's ancestral home was in Changzhou, Jiangsu. Because he moved around a lot as a child, he learned to speak four different Chinese dialects by the time he was 12. In 1910, Chao went to the United States with a Boxer Indemnity Scholarship to study mathematics and physics at Cornell University, where he was a classmate and lifelong friend of Hu Shih (1891–1962), the leader of the New Culture Movement. He then became interested in philosophy; in 1918, he earned a PhD in philosophy from Harvard University with a dissertation entitled "Continuity: Study in Methodology".

Already in college his interests had turned to music and languages. He spoke German and French fluently and some Japanese, and he had a reading knowledge of Ancient Greek and Latin. He was Bertrand Russell's interpreter during Russell's visit to China in 1920. In My Linguistic Autobiography, Chao wrote of his ability to pick up a Chinese dialect quickly, without much effort. Chao possessed a natural gift for hearing fine distinctions in pronunciation that was said to be "legendary for its acuity", enabling him to record the sounds of various dialects with a high degree of accuracy.

In 1920, Chao returned to China and taught mathematics at Tsinghua University. The next year, he returned to the United States to teach at Harvard University. In 1925, he again returned to China, teaching linguistics and music courses at Tsinghua, and in 1926 began a survey of the Wu dialects. While at Tsinghua, Chao was considered one of the 'Four Great Teachers / Masters' of China, alongside Wang Guowei, Liang Qichao, and Chen Yinke.

He began to conduct linguistic fieldwork throughout China for the Institute of History and Philology of Academia Sinica from 1928 onwards. During this period of time, he collaborated with Luo Changpei, another leading Chinese linguist of his generation, to translate Bernhard Karlgren's Études sur la Phonologie Chinoise (published in 1940) into Chinese.

In 1938, he left for the US and resided there afterwards. In 1945, he served as president of the Linguistic Society of America, and in 1966 a special issue of the society's journal Language was dedicated to him. In 1954, he became an American citizen. In the 1950s he was among the first members of the Society for General Systems Research and he also participated in the Macy conferences. From 1947 to 1960, he taught at the University of California at Berkeley, where in 1952, he became Agassiz Professor of Oriental Languages.

While in the United States in 1921, Chao recorded Old National Pronunciation gramophone records, which were then distributed nationally as proposed by Commission on the Unification of Pronunciation as part of its failed campaign to manufacture a unified Standard Chinese.

He is the author of one of the most important standard modern works on Chinese grammar, A Grammar of Spoken Chinese, which was translated into Chinese separately by Lü Shuxiang in 1979 and by Ting Pang-hsin in 1980. It was an expansion of the grammar chapters in his earlier textbooks, Mandarin Primer and Cantonese Primer. He was co-author of the Concise Dictionary of Spoken Chinese, which was the first dictionary to characterize Chinese characters as bound or free—usable only in polysyllables or permissible as a monosyllabic word, respectively.