William Valentine Mayneord (1902-1988) was a British radiologist and pioneer in the field of medical physics. He first entered the field in 1924, at St. Bart's Hospital in London, when radiotherapy was just becoming recognized. Later he moved to the Cancer Hospital, which is now the Royal Marsden Hospital. He was elected a Fellow of the Royal Society in 1965 and wrote the book Carcinogenesis and Radiation Risk.