William Belmont Parker (born Hasbury, England, 19 September 1871; died 1934) was a United States editor.
He came to the United States in early youth, graduated from Harvard in 1897, and in 1898-1902 was assistant editor of the Atlantic Monthly.
He was literary adviser to Houghton, Mifflin and Company, New York City, in 1902-04; instructor in English at Harvard in 1904-05 and lecturer in that subject at Columbia in 1905-08.
He was editor and literary adviser to the Baker and Taylor Company in 1909-12, and literary adviser to the Century Company in 1912.
Beginning in 1914, he was an editor with S. Pearson and Son.