William Roscoe Thayer (1859–1923) was an American author and editor. He graduated from Harvard in 1881, and became editor of the Harvard Graduates' Magazine in 1892. In 1914 he was elected to The American Academy of Arts and Letters, and he received honorary degrees from Harvard, Yale, Brown, and other universities. His verse includes:

• The Confessiones of Hermes (1884)
• Hesper, an American Drama (1888)
• Poems, New and Old (1894)

In prose he wrote, amongst other works:

• The Dawn of Italian Independence (1893)
• History and Customs of Harvard University (1898)
• Throne-Makers (1899)
• A Short History of Venice (1905)
• Life and Times of Cavour (two volumes, 1911)
• Life and Letters of John Hay (1915)
• Germany vs. Civilization (1916)