"You Light Up My Life" is both a Grammy Award and an Academy Award winning ballad written by Joe Brooks and originally recorded by the late Kasey Cisyk for the soundtrack to the film of the same name. The song was performed in the film by its lead, Didi Conn, who lip synched Cisyk's version. Pat Boone's daughter, Debby Boone, was recruited to record the single, which became a massive success, topping the Billboard Hot 100 chart for a record-setting ten consecutive weeks. It easily became the most successful single of the 1970s in the United States and set a new Hot 100 record for longest reign at No.1. (Elvis Presley's double-sided "Don't Be Cruel/Hound Dog", then recognized as the longest-running No.1 of the Rock Era, spent 11 weeks atop the Billboard Best Sellers chart in 1956, before the debut of the Hot 100.) The record was matched in 1982 by Olivia Newton-John's Physical, but never surpassed until a 1991 change in chart methodology allowed songs to achieve longer reigns at No.1 ("End of the Road" by Boyz II Men set the new record, 13 weeks). The single, which was certified platinum by the RIAA, also hit #1 on the Adult Contemporary chart and even reached #4 on the Country chart. Although written by Brooks as a love song, the devout Boone interpreted the song as inspirational and proclaimed that it was instead God who "lit up her life."

Cisyk's soundtrack recording was released as a single to bolster sales of the soundtrack after Boone included her version on her first solo album also entitled You Light Up My Life. (Although the soundtrack was certified gold, peaking at No. 17 on the Billboard 200 albums chart, it never included Boone's version of the song.) Cisyk's single was credited to "Original Cast", not to Cisyk herself, and only reached No. 80 on the Billboard Hot 100. Brooks also released an instrumental version of the song from the soundtrack as a single, but his version failed to chart. Boone's success resulted in Grammy nominations for Best Pop Vocal Performance Female and Record of the Year and won her the 1977 Grammy for Best New Artist and the 1977 American Music Award for Favorite Pop Single. The song earned Brooks the 1977 Song of the Year Grammy (tied with "Love Theme from "A Star Is Born" (Evergreen)") as well as the Best Original Song awards at the 1977 Golden Globe and Academy Awards.

The song ranks #7 on Billboard's All Time Top 100.[1]

Many artists have covered "You Light Up My Life" since 1977. The following year, Johnny Mathis recorded and named his album after the song. LeAnn Rimes released her version as a single in 1997 – 20 years after Boone's version was released and on the same record label (Curb Records). Her version fared modestly by comparison to the original at radio (No. 34 Pop, No. 48 Country). However, her single was certified gold and was the title track to her No. 1 Pop and Country album, You Light Up My Life: Inspirational Songs.

Among the other diverse artists who have recorded and/or performed the song are:

The song was also parodied in the Six Feet Under episode The Rainbow of Her Reasons.