"One Fine Day" is a song written by Gerry Goffin and Carole King. It first became a popular hit in the summer of 1963 for the American girl group The Chiffons, who reached the top five on the Billboard Hot 100 chart. In 1980, King covered her own song and charted at number 12 on the Hot 100 with her version. The song has subsequently been covered by numerous artists over the years.

Goffin and King were inspired by the title of the aria "Un bel di vedremo" from the Puccini opera Madama Butterfly. Intended for Little Eva, "One Fine Day" was prepped as a demo by Goffin and King with King providing a guide vocal but – despite a propulsive piano riff courtesy of King – Goffin and King were unable to construct a viable arrangement and eventually gave up, passing the song to The Tokens who had recently produced the #1 hit "He's So Fine" by The Chiffons for whom it was thought another "fine" song had hit potential. The piano work by King (whose vocal was erased) was retained for The Chiffons' recording and King attended the session at which The Chiffons recorded their vocals. However the Tokens radically re-worked the Goffin/King demo of "One Fine Day" for The Chiffons' version; Gerry Goffin commented that the Tokens "really earned their production credit". The personnel on the original recording included Carl Lynch on guitar, Dick Romoff on bass, Artie Kaplan, Sid Jekowsky, and Joe Grimaldi on sax, and Gary Chester and Buddy Saltzman on drums.

"One Fine Day" by The Chiffons reached #5 on the Billboard Hot 100: its R&B chart peak was #6. The single was an international hit charting in the UK (#29),France (#18), and New Zealand (#6). The Chiffons' "One Fine Day" was ranked #460 on Rolling Stone Magazine's list of The 500 Greatest Songs of All Time.

The Chiffons' placing two "fine" songs in the Top Ten motivated The Tokens to especially prep the group's next single "A Love So Fine" which only managed a #40 peak.

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