The songs "One Hand, One Heart" and "A Boy Like That/I Have a Love" were performed live on set by Ansel Elgort and Rachel Zegler & Ariana DeBose and Zegler respectively. Sections of "Maria" were also sung live on set by Elgort, as per his request. All other songs were filmed to the more traditional playback technique. "Somewhere" was also sung live on set by Rita Moreno.
John Williams was brought in to serve as music consultant for the film. Williams was piano soloist for the soundtrack of the 1961 version.
According to a behind-the-scenes featurette of the film, Steven Spielberg explained why he always wanted to direct a motion picture adaptation of the original 1957 Broadway musical production: "I have been challenged by what would be the right musical to take on. And I could never forget my childhood. I was 10 years old when I first listened to the West Side Story album, and it never went away. I've been able to fulfill that dream and keep that promise that I made to myself: You must make West Side Story." He, then, went on to explain why the musical is even more topical in modern times than it was when the musical first premiered on Broadway: "Divisions between un-likeminded people is as old as time itself," Spielberg said. "And the divisions between the Sharks and the Jets in 1957, which inspired the musical, were profound. But not as divided as we find ourselves today. It turned out in the middle of the development of the script, things widened, which I think in a sense, sadly, made the story of those racial divides - not just territorial divides - more relevant to today's audience than perhaps it even was in 1957."
Considering the relatively large 60-year time span between the original and this production, three actors who appeared in the 1961 release reprise different roles in this 2021 production, including, Rita Moreno, Harvey Evans and David Bean. Evans and Bean were both members of "The Jets" in the original, respectively playing Mouthpiece and Tiger. Evans passed away two weeks after this film's release.
Contrasting with most modern movie musicals, almost the entirety of the cast is made up of musical theatre performers unknown to mainstream film audiences. Rita Moreno is the most famous among the lead cast, being an EGOT winner. Except for Ansel Elgort (who became famous through non-musical films), Rachel Zegler (who got cast straight out of high school), and Corey Stoll (who's worked primarily on TV with a few supporting film roles), all of the principals are Broadway alums.