William Henry Young FRS (London, 20 October 1863 – Lausanne, 7 July 1942) was an English mathematician. Young was educated at City of London School and Peterhouse, Cambridge. He worked on measure theory, Fourier series, differential calculus, amongst other fields, and made contributions to the study of functions of several complex variables. He was the husband of Grace Chisholm Young, with whom he authored and co-authored 214 papers and 4 books. Two of their children became professional mathematicians (Laurence Chisholm Young, Cecilia Rosalind Tanner). Young's Theorem was named after him.
In 1913 he was the first to be appointed to the newly created chair of Hardinge Professorship of Pure Mathematics in Calcutta University which he held from 1913 to 1917. He also held the part-time Professorship of Philosophy and the History of Mathematics at the University of Liverpool from 1913 to 1919.