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Yum-Tong Siu (simplified Chinese: 萧荫堂; traditional Chinese: 蕭蔭堂; pinyin: Xiāo Yìntáng; born May 6, 1943 in Guangzhou, China) is the William Elwood Byerly Professor of Mathematics at Harvard University.

Dr. Siu has been the dominant figure in the mathematics of several complex variables, for a quarter-century. He has mastered techniques at the interfaces between complex variables, differential geometry, and algebraic geometry. For example, he applied estimates of the complex Neumann problem and the theory of multiplier ideal sheaves to algebraic geometry, to resolve various conjectures. (cf. MSRI Publications, Vol. 37: Several Complex Variables)

Siu's education included a BA in mathematics from the University of Hong Kong, M.A. from the University of Minnesota and Ph.D. from Princeton University, in the period 1963–1966. He started his academic career as Assistant Professor in Purdue and Notre Dame Universities, but rose fast in the ranks and became full Professor at Yale and then Stanford Universities. In 1982 he joined Harvard as Professor, and in 1992 became the William Elwood Byerly Professor. In addition he was former Chairman of the Harvard Math Department He lives in the Greater Boston area.

He has received numerous recognitions including invited addresses at three International Congresses of Mathematicians (Helsinki, 1978; Warsaw, 1983; Beijing, 2002); Bergman Prize of the American Mathematical Society; honorary doctorates at the universities of Hong Kong and Bochum, Germany. He had also served as Associate Editor of the Annals of Mathematics, and Editor of the Journal of Differential Geometry.

As of May, 2006, he was elected to the Advisory Committee for the Millennium Prize Problems under the sponsorship of the Clay Mathematics Institute.

In 2006, Siu published a proof of the finite generation of the pluricanonical ring.[1]