"September" is a song by the American band Earth, Wind & Fire released as a single on November 18, 1978, by ARC/Columbia Records.

[1] The song was written by Allee Willis and Maurice White, based on a music sequence developed by guitarist Al McKay.

[5] The song remains a staple of the band's body of work and has been sampled, covered, remixed, and re-recorded numerous times.

[6] "September" has a funk groove based on a four-measure pattern that is consistent between verses and choruses, built on a circle of fifths.

Willis was initially bothered by the gibberish "ba-dee-ya" lyric White used through the song, and begged him to rewrite it: "I just said, 'What the fuck does 'ba-dee-ya' mean?'

[9] Although several theories about the significance of the date have been suggested, the songwriter Maurice White claimed he simply chose the 21st due to how it sounded when sung.

[21] Earth, Wind & Fire recorded a new version of the song, retitled "December", for their 2014 Christmas album Holiday.

"September" has had renewed interest in the 21st century and has been an Internet meme as well as the source of original content by social media users.

The 2019 film Polar features the song playing during its opening sequence, with the characters singing along to it together after pulling off a successful hit.

A remix of the song by English dance music duo Phats & Small[63] called "September '99" was issued in 1999 on the compilation album The Ultimate Collection.

"[90] Mike Joseph of PopMatters said "Kirk Franklin takes the band's 'September' (literally, by sampling the original version) and refashions it into an anthem of survival, using 'September' as a metaphor for a time when things aren't going so well, and using his talented choir of singers to give the lyrics a jubilant reading.