Those familiar with Leonard Bernstein's West Side Story are generally aware that it is an updating of Shakespeare's tragic love story Romeo and Juliet. "Tonight" is one of the most popular songs from this 1957 Broadway musical smash hit. It is a duet sung by lovers Tony and Maria, and features one of Bernstein's best-known and -loved melodies. In the story it comes in the famous balcony scene, right after Tony meets Maria, and shortly after he sings the equally popular song "Maria." It reappears later on, in the quintet scene, truncated and with different lyrics.
"Tonight" begins with an introductory section where, in the latter moments, the music works up passionately to the dramatic first appearance of the song's famous melody. Maria introduces it: two notes rise on the first "Tonight," then descend on the second one, after which the melody soars to the heavens with a sense of passion and drama, of being carried away. Then Tony takes up the song's second subject, bringing music of equal beauty, even if its sense of passion is reined in a bit. The lovers sing softly and more slowly in a brief central episode, but soon the melody regains its animation and emotional sweep, the dazzled pair realizing their mutual love ("Tonight, tonight the world is wild and bright, going mad shooting sparks into space"). This passionate duet appropriately ends softly and intimately, recalling the hushed atmosphere from its opening.