The music is composed by Leonard Bernstein with lyrics by Stephen Sondheim and takes a phrase from the slow movement of Beethoven's 'Emperor' Piano Concerto, which forms the start of the melody, and also a longer phrase from the main theme of Tchaikovsky's Swan Lake.

In the stage musical, the song appears in the second act of the show during the Somewhere Ballet. It is performed by an off-stage soprano singer and is later reprised by the entire company. At the end of the show, when Tony is shot, Maria sings the first few lines of the song as he dies in her arms.