William Hinsche (June 29, 1951 – November 20, 2021) was an American musician who was a co-founding member of the singing trio Dino, Desi & Billy and a keyboardist for the Beach Boys' backing band.

Hinsche attended Beverly Hills Catholic School, where he met Desi Arnaz, Jr. and Dean Paul Martin.

Although he declined at least one offer to formally join the group in favor of continuing his education in August 1969, he toured extensively with the band as a vocalist and multi-instrumentalist (often playing keyboards and rhythm guitar) from 1971 to 1977 and 1982 to 1996.

Billy Hinsche provided backing vocals on recordings for Elton John's "Don't Let The Sun Go Down On Me," Warren Zevon's "Desperados Under The Eaves," America's "Hat Trick," Joan Jett's "Good Music" and others.

Featured Dennis Diken (The Smithereens) on drums, David Marks (co founding member of The Beach Boys), Robert Lamm (Chicago), Jeffrey Foskett (Brian Wilson, Beach Boys), and Charlotte Cooper (Lucky Guy on Spotify).