"Where or When" is a show tune from the 1937 Rodgers and Hart musical Babes in Arms. It was first performed by Ray Heatherton and Mitzi Green. That same year, Hal Kemp recorded a popular version. It also appeared in the movie of the same title two years later. Dion and the Belmonts also released a successful remake of the song, which reached number 3 on the Billboard Hot 100 in January 1960. In 1963, The Lettermen released their version as a single, which peaked at number 98 on the Hot 100. The song was used for the 1992 biopic Sinatra, starring Philip Casnoff; Frank Sinatra performs the song on stage at the Paramount Theatre.

"Where or When" is the first number to appear in the original Broadway production of Babes in Arms. The musical opens in Seaport, Long Island, on a hectic morning that finds most of the adult population embarking on a five-month vaudeville tour. Soon after his parents' departure, twenty-year-old Valentine LaMar (played by Ray Heatherton) discovers at his doorstep a young hitchhiker named Billie Smith (played by Mitzi Green). Instantly smitten, he engages her in a discussion of movie stars, self-defense maneuvers, and Nietzsche's theory of individualism, at which point Val impulsively steals a kiss. Both admit to a powerful sense of déjà vu and sing "Where or When" as a duet.MGM bought the screen rights to Babes in Arms in 1938, and the following year the studio released a film with that title, starring Mickey Rooney and Judy Garland, that bore little resemblance to its stage predecessor; the characters and plot were substantially revised (by ten studio writers), and only two numbers were retained from the score. "Where or When" was one that survived, appearing 37 minutes into the film, sung by Betty Jaynes, Douglas McPhail and Garland in a scene depicting a rehearsal sequence, although Garland is cut short during her performance.

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