William Richard LeFanu FSA (9 July 1904 - 1 April 1995) was an Irish librarian. He was the husband of composer Elizabeth Maconchy.
LeFanu was born in Ireland, the son of Thomas Philip Le Fanu and his wife Florence Sophia Mabel (née Sullivan). He was educated in England at Eton and King's College, Cambridge.
In 1930, he married the composer Elizabeth Maconchy (later Dame Elizabeth Maconchy); they had two daughters, Elizabeth Anna (known as Anna, born 1939) and Nicola LeFanu (born 1947).
LeFanu worked for almost forty years as librarian at the Royal College of Surgeons in London.