"September" is a song by American funk band Earth, Wind & Fire, written by Maurice White, Al McKay, and Allee Willis. It was recorded during the I Am sessions and released as a single in 1978. Featured on the band's album The Best of Earth, Wind & Fire, Vol. 1, "September" reached number one on the US R&B chart, number eight on the Billboard Hot 100, and number three on the UK singles chart.

There is no evidence that White's unusual lyrics for the chorus have any concrete meaning (whether as a reference to the Persian king Bardiya, said to have been murdered in September 522 B.C., or otherwise), and were questioned by Willis: "I said, 'We are going to change 'ba-dee-ya' to real words, right?' ... I learned my greatest lesson ever in songwriting from him, which was never let the lyric get in the way of the groove."

The song is performed in the key of A major with a tempo of 126 beats per minute in common time. The group's vocals span from E₄ to F♯₅.

The song was certified silver by the British Phonographic Industry and certified gold in the US (Until the RIAA lowered the sales levels for certified singles in 1989, a Gold single equaled 1 million units sold.) "September" was later certified Gold for digital sales by the RIAA, and has sold over 2 million digital copies in the US as of September 2017. The song was also later released as "December", chord changes & melody remained identical, with lyrics re-written for the "...Twenty-fifth of December...", performed by Earth Wind & Fire, as well, on a later album.

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