William Alwyn (November 7, 1905 – September 11, 1985) was an English composer.

He was born in Northampton and educated at the Royal Academy of Music. He was for a time the principal flutist for the London Symphony Orchestra, as well as teaching at the Royal Academy. He was very versatile and was a distinguished linguist, poet, and artist, as well as musician.

His compositional output is varied and large, including five symphonies, two operas, several concertos and string quartets, and over 60 film scores. His most famous film scores are for Odd Man Out, Dear Victory, and Fires Were Started. Alwyn's concerto for harp and string orchestra, Lyra Angelica, became popularly known when figure skater Michelle Kwan performed to it at the 1998 Winter Olympics.

He died in Southwold, England.