William Alan Finn (February 28, 1952 – April 7, 2025) was an American composer and lyricist. He was best known for his musicals, which include Falsettos, for which he won the 1992 Tony Awards for Best Original Score and Best Book of a Musical, A New Brain (1998), and The 25th Annual Putnam County Spelling Bee (2005).

Finn was born in Boston, Massachusetts, on February 28, 1952. He was Jewish, raised in conservative Judaism, and grew up in Natick, Massachusetts, with his parents and siblings, Michael and Nancy. He attended the Temple Israel in Natick, where his rabbi was Harold Kushner. In Hebrew school, Finn wrote his first play, and said, "I don't think I ever told anyone this: The first play I ever wrote was in Hebrew. I have no idea what it was about. But it was horrible, I guarantee it. I couldn't write plays, and I couldn't really speak Hebrew, so how good could it be?" While attending Natick High School, Finn competed with the Natick Speech Team and was in the drama department headed by Gerald Dyer. For his bar mitzvah, he received a guitar and taught himself to play.

He went on to attend Williams College in Williamstown, Massachusetts, as a music major. He originally entered as a guitar major, "When I got to college I kind of transferred to the piano. I transferred what I knew on the guitar to the piano. But when I was playing the guitar I was always writing my own songs — and singing a few of — I only had one book of folk songs, a blue book, of these sad, sad folk songs. ...I would start them the way they were written and then I would change them to how I wanted them.... I would just use the lyrics — re-musicalize the lyrics." When he graduated, he received the Hutchinson Fellowship (a musical composition award).

Finn was a heavily autobiographical writer; he always wrote his own lyrics. His topics included the gay and Jewish experiences in contemporary America, and also family, belonging, sickness, healing, and loss. According to a 2006 article, "The Washington Post called him 'the composer laureate of loss.'"

Finn was especially noted for his work on what was to become a trilogy of short musicals Off-Broadway. In Trousers, March of the Falsettos, and Falsettoland. All of them chronicle the lives of the character Marvin; his ex-wife, Trina; his boyfriend, Whizzer; his psychiatrist, Mendel; and his son, Jason. Falsettos, the combination of the latter two parts of his Marvin Trilogy (March of the Falsettos and Falsettoland), opened on Broadway at the John Golden Theater on April 29, 1992, and ran for 486 performances. It went on to garner seven nominations at the 46th Tony Awards, winning two: the 1992 Tony Award for Best Original Score as well as the 1992 Tony Award for Best Book of a Musical, the latter Finn shared with James Lapine.

A critically acclaimed revival opened on September 29, 2016, at the Walter Kerr Theater and went on to garner five nominations at the 71st Tony Awards, including Best Revival.

With Lapine, Finn penned a musical loosely based on his near-death experience following brain surgery, exploring the role of music in his life and recovery. The musical's main character is a man who has what may be a terminal arteriovenous malformation (AVM). Finn's longtime partner, Arthur Salvadore, is represented by the character Roger Delli-Bovi. Finn's mother is also present in the piece. That musical, A New Brain, starred Malcolm Gets, Kristin Chenoweth and Chip Zien, and premiered at the then Off-Broadway venue, the Lincoln Center Theater in 1998. The musical won the 1999 Outer Critics Circle Award for Outstanding Off-Broadway Musical. The UK premiere was at the 2005 Edinburgh Festival Fringe.

At the 2006 Elliot Norton Awards Ceremony, Finn brought his high school drama teacher, Gerry Dyer, onstage with him to present an award. Finn said of Dyer that he "imbued us with a ridiculous sense of our own self-worth." Another student of Gerald Dyer, Alison Fraser, found fame on Broadway, collaborating with Finn in the original casts of In Trousers and March of the Falsettos.