Denis ApIvor (April 14, 1916 – May 27, 2004) was a British composer. He belonged to the generation of modernists that included Humphrey Searle and Elisabeth Lutyens.
Born in County Westmeath, Ireland, to Welsh parents, he studied medicine in London, but had pursued the study of music from an early age. He studied composition with Alan Rawsthorne and Patrick Hadley. His most successful early works included a setting of T. S. Eliot's The Hollow Men (1939), several ballets, including A Mirror for Witches (1952) and Blood Wedding (1953), and an opera, Yerma (1954). Around 1960, he began composing in a serialist style, and this continued until the late 1980s, when he returned to diatonic composition.
ApIvor is particularly well known to guitarists, as he made a major contribution to the repertoire of their instrument. Solo works include Variations (1959), Discanti (1970), Saeta (1972), and ten serial pieces included with his book Serial Composition for Guitarists (1982). He also wrote a Concertino for guitar (1954), Liaison for guitar and keyboard (1976), and Cinquefoil for flute, guitar, and viola (1984).