Early in 1949, Jerome Robbins called Leonard Bernstein with what the composer called "a noble idea: a modern version of Romeo and Juliet set in the slums at the coincidence of Easter-Passover celebrations." The two men had worked together on the groundbreaking musical On the Town (which was being turned into a movie for MGM that year) and they were excited about the as-yet untested possibilities of telling a tragic story "using only musical-comedy techniques, never falling into the "operatic" trap," Bernstein said in the diary he published in 1957. By mid-April, they had a writer, Arthur Laurents, and a draft of the first four scenes. At that point, it was called "East Side Story" and focused on Christian-Jewish conflicts on the lower East Side. Various individual projects for the two collaborators kept delaying completion of the play, but they continued to work on the musical over the next few years, even though often it was a long-distance relationship. A young composer and lyricist, Stephen Sondheim, was added to the mix, and the result was a collaboration built, as Laurents said in his autobiography, on mutual admiration, respect and affection. Bernstein and Sondheim particularly enjoyed working together, composing in separate rooms of Bernstein's apartment. Then after an hour or so, they would get back together to compare and refine their work. "The whole experience was a wonderful sort of musical exchange: what we gave each other, took from each other, yielded to each other," Robbins said.

In 1955, Laurents came up with the idea of moving the story to the upper West Side and turning the rivals into black and Puerto Rican gangs, a troubling phenomenon just beginning to hit the news. The others went for the idea wholeheartedly (although the black gang was eventually turned into a gang of white working-class teens). Laurents imposed on himself the constraint of sticking very closely to Shakespeare's original as he completed what turned out to be one of the shortest books for a musical on record. Besides the two young lovers as the leads, he kept Juliet's confidante, the Nurse (who became her friend Anita), the sympathetic Friar character (Doc, the candy store owner), Romeo's friend Mercutio (Riff), and his enemy, Juliet's cousin Tybalt (Maria's brother Bernardo). At last - after clearing the considerable hurdles in securing backers for a musical so full of violence, anger, and racial tension - the play opened on Broadway on September 26, 1957.

"What we really did stylistically with West Side Story was take every musical theater technique as far as it could be taken. Scene, song and dance were integrated seamlessly; we did it all better than anyone ever had before," Laurents wrote in Original Story By (Knopf, 2000). "We were not the innovators we were called, but what we did achieve was more than enough to be proud of." The same might be said about the film version - but not by Laurents. He disliked the film, saying it was overblown and that "only the vitality of the music survived." But he did acknowledge that West Side Story might have faded into history if it hadn't been for the movie. Sales of the Broadway cast album were minimal; almost no popular singers had picked up the songs for concert or airplay, which always boosted a show's popularity. Sales of the soundtrack album, however, went through the roof, and soon everyone was singing "Tonight." Any money the collaborators made on West Side Story came from the film and not the stage musical.

For the task of adapting the musical to the screen, the producers turned to veteran filmmaker Robert Wise (brought in as co-director to offset Robbins' lack of film experience) and screenwriter Ernest Lehman. To translate the highly stylized look and feel of the play to the realism demanded by film audiences, it was decided to set the story in actual New York locations and to choreograph the numbers on the streets for free, spontaneous movement (which, if anything, brought a greater dynamic to Robbins' work). That meant songs like "Something's Coming" and "The Prologue," previously performed on the stage in stylized settings, were situated in recognizable New York locations.

Lehman stuck closely to Laurents' original script but made enough changes to merit a screenwriting credit. Among other things, he repositioned several of the songs and chose new settings for some of them. The satirical "Officer Krupke" was placed sooner in the show and outside the candy store instead of inside. "Cool" was positioned later in the story, after the rumble, and inside a garage with an oppressively low ceiling over the performers' heads, adding to the tension of the piece. Lehman thought "I Feel Pretty" stopped the dramatic action of the show in its original placement, so he moved it back toward the beginning. None of these changes were made without some intense wrangling, especially with Robbins. Still, while most of these alterations were handled amicably, the troubles that cropped up in the scripting process were just the beginning of a tense film set that was just the opposite of the more idyllic theatrical collaboration.