Chevalier William Henry Grattan Flood (baptised 1 November 1857 – 6 August 1928) was a noted Irish author, composer, musicologist, and historian. As a writer and ecclesiastical composer, his personal contributions to Irish music produced enduring works, although he is regarded today as controversial due to the inaccuracy of some of his work. As a historian, his output was prolific on topics of local and national historical or biographical interest.