Sir William Henry St John Hope (1854–1919) was an English antiquary.
Hope was born in Derby, the son of the Reverend William Hope, vicar of Saint Peter's Church. He was educated at Derby Grammar School and at Peterhouse, Cambridge. On leaving Cambridge, he became a master at Rochester Grammar School in Kent, a post he continued to hold until his appointment in 1885 as Assistant Secretary of the Society of Antiquaries.
Interested in archaeology and heraldry since boyhood, his earliest works were on the subject of the monumental brasses often found in English churches. His largest and most important work was his Architectural History of Windsor Castle, began in 1893 with the approval of Queen Victoria, and completed twenty years later in 1913, an undertaking for which he was knighted. His other works include Stall-plates of Knights of the Garter, Heraldry for Craftsmen and Designers and A Grammar of English Heraldry.
He was involved in the Society of Antiquaries's report on the restorations and alterations at Bath by Charles Davis in the 1880s. His 1899 English Altars was the first publication of the Anglican traditionalist Alcuin Club. He assisted Sir Harold Brakspear in investigating Ludlow Castle in 1903 and in drawing the plans of Lewes Priory in 1906. Between 1909 and 1915, he participated in the first major excavation of the hillfort at Old Sarum, along with William Hawley and Duncan Montgomerie.