This article refers to the song "Moon River". For other references, see Moon River (disambiguation).

"Moon River" is a song composed by Johnny Mercer and Henry Mancini in 1961. It was sung in the movie Breakfast at Tiffany's by Audrey Hepburn, the movie's star, while the song itself won that year's Academy Award for Best Song for Mercer and Mancini. The success of the song was responsible for re-launching Mercer's career as a songwriter, which had stalled in the mid-1950s as rock and roll replaced jazz standards as the popular music of the time.

Mercer and Mancini originally wrote the song for Hepburn to fit the actress' limited vocal range (Hepburn was not an accomplished and established singer). "Moon River" is introduced by Hepburn during the sequence where George Peppard's character, Paul 'Fred' Varjak, discovers Holly Golightly (Hepburn) singing (with guitar in hand) on the ledge of her apartment during a rainstorm.

Although an original score album to "Tiffany's" was released, it did not contain Hepburn's original version. Instead, an album version recorded by Mancini and his chorus was released as a single and became a Top 40 hit. Subsequently, it was released by UK singer Danny Williams, who got a UK #1 with it. Shortly thereafter, Andy Williams would make the song an even bigger hit (even going as far as making it his theme song). Many other artists have recorded it since. It was only months after Hepburn's death in 1993 that the original version was finally released on an album. Despite Williams' success with the song, for many Hepburn's simple recording is considered the definitive performance.

An inlet near Savannah, Georgia, Johnny Mercer's hometown, was named "Moon River" in honor of this song. Williams later named his production company and venue in Branson, Missouri after this song, whose lyrics read:

Moon River, wider than a mile

I'm crossing you in style someday

Oh, dream maker, you heartbreaker,

Wherever you're goin',

I'm goin' your way

Two drifters off to see the world

With such a lot of world to see

We're after the same rainbow's end

Waitin' 'round the bend

My huckleberry friend, Moon River, and me.

• In the movie, Holly and Paul perform some petty shoplifting at a five and dime store, stealing a pair of plastic Halloween masks. Appropriately, Holly's mask is that of cartoon character Huckleberry Hound, a reference to the "huckleberry friend" of the song.