A young couple from dueling street gangs falls in love.

In the slums of the upper West Side of Manhattan, New York, a gang of Polish-American teenagers called the Jets compete with a rival gang of recently immigrated Puerto Ricans, the Sharks, to "own" the neighborhood streets. The tension between them is marked by their bullying and tormenting of one another, and when a series of incidents erupts into a fistfight on a playground, two policemen, the bigoted Lt. Schrank and Officer Krupke, arrive in time to break it up. Afterward, Riff, the leader of the Jets, suggests to his companions that they settle their differences with the Sharks once and for all by challenging them to a "rumble," which is their term for a street fight. Although Riff warns that the Sharks may choose to fight with zip guns or knives rather than fists, the Jets are enthusiastic about his idea. For support, Riff meets with Tony, a former member of the Jets who is like a brother and who now works in a candy store owned by good-hearted Doc. Riff asks Tony to attend a dance at the gym, an area considered neutral territory where Riff can present the challenge to Bernardo, the Shark's leader. Tony, who has lost interest in promoting violence, reluctantly agrees to accompany him out of friendship. When Tony confides that he has been having premonitions that something special is about to happen to him, Riff suggests that it may be waiting for him at the dance. Meanwhile, Bernardo's younger sister Maria and his girl friend, Anita, both of whom work at a bridal shop, are finishing a dress for Maria to wear to the dance, which will be her first since immigrating to America a month earlier. Although Bernardo has hopes of her marrying his comrade Chino, Maria tells Anita that she does not have special feelings for her brother's friend. That evening, at the gym where the dance is held, Bernardo is introducing Maria to other Puerto Ricans, when several members of the Jets arrive. Both gangs are poised to fight, when Glad Hand, the social worker, and Krupke intervene. The dancing continues and soon becomes a competition between the rival gangs and their women, who refuse to intermingle. From opposite sides of the dance floor, Tony and Maria spot each other and, entranced, move toward each other and begin to dance. Seeing them together, Bernardo protectively pulls Maria away, telling her that Tony is only interested in sexual favors, and orders Chino to take her home. Before Bernardo leaves, he and Riff agree to meet later at Doc's for a "war council," where they will determine the time and place of the rumble. At his family's apartment, Bernardo lectures Maria about the dangers in America, but Anita half-jokingly scolds him, saying that in their new country, women are free to see whom they wish. Anita and Bernardo meet with their friends on the rooftop, where they engage in a lively discussion about the pros and cons of living in America. Although the women tease the men that life in America is better than in their home country, the men complain that it is only better if you are white. Meanwhile, Tony walks the streets in a daze, bewitched by the thought of Maria. She is in her room, preparing for bed, when she hears Tony calling out her name from the alley below and climbs through the window to the fire escape to be with him. Believing that Maria is the fulfillment of his premonition, Tony is eager to acknowledge publicly his love for her, but Maria is aware that their families will not approve. After admitting their love for each other and marveling at how their lives have changed in one evening, they part, agreeing to meet the next day at the bridal shop after closing time. At Doc's shop, the Jets are restlessly waiting for the Sharks to arrive, when the police drive up. Although Krupke is suspicious that the gang is up to mischief, he is called away and the boys then make fun of him, as well as social workers, judges, psychiatrists and all those who have failed to alleviate the poverty and violence in which they have been reared. When the Sharks arrive, the two gangs decide the time and location of the fight, but as they discuss weapons, Tony, who has by then returned to help close the shop for the evening, convinces them to have a "fair fight," using nothing but fists. Schrank enters, prompting the two gangs to pretend to get along, and demands to know what they are planning. When no one will talk to him, he harasses the Puerto Ricans, ordering them out, and then tells the Jets that he wants his beat clear of the immigrants as much as they do. When the Jets still refuse to confide in him, he tauntingly refers to their family members as drug addicts and prostitutes. After everyone leaves the shop, Doc expresses his dismay at Schrank's behavior, but Tony, who is buoyed by love, believes that everything will be all right. The next day, Maria's co-workers notice her happiness and she admits that she feels "pretty." Anita is still at the shop when Tony arrives, but grudgingly allows them time together. Although Tony has no plans to attend the fight, Maria urges him to go and stop it from happening. Then, they playfully pretend to have a wedding, with store mannequins in attendance. Later, in the evening, the Jets and the Sharks prepare for the rumble, while Anita prepares for a romantic interlude with Bernardo when he returns. While helping Doc, Tony can think of nothing but Maria, who is at home, waiting impatiently for the end of the evening, when she and Tony can be together. At the appointed place, the Sharks and the Jets meet, and the best fighter from each gang, Bernardo and Ice, respectively, prepare to fight as the others look on. When Tony arrives, his efforts to stop the fight inadvertently escalate the battle into a knife fight between Riff and Bernardo. When Bernardo unexpectedly kills Riff, Tony, in a fit of passion, takes the dead Riff's knife and stabs Bernardo. Although Tony is immediately overcome with shame for killing Maria's brother, the other gang members join the fight, but all flee when they hear the sound of a police siren. Waiting on the rooftop for Tony, Maria is surprised when Chino arrives to tell her that Tony killed Bernardo. Praying that he is lying, Maria runs to her room and finds Tony, who confesses. Although she wants to hate him, she finds she cannot and says that the problem is not with either of them, but everything around them. Together, they envision a place where they can go that is free of prejudices. Outside, the police cruise the streets, but the gang members evade them. The Jets meet, stunned, because they never expected anyone would be killed. When their anxiety leads to internal bickering, Ice, who is now their leader, tells them to be "cool." When they learn from an eavesdropping tomboy, Anybodys, that Chino is carrying a gun and bent on revenge against Tony, they organize to protect him. Anita, who discovers that Maria has been with Tony, is offended that she would remain faithful to a boy who would kill her brother, but is soon won over by Maria's love for Tony and warns her about Chino's mission. Although Maria and Tony had planned to rendezvous at Doc's and leave town together, when Schrank detains Maria to question her about Bernardo's death, Anita agrees to tell Tony that she will soon be with him. However, when Anita enters the candy store, the Jets, suspicious of her motives, prevent her from finding Tony, then attempt to rape her. Doc enters in time to stop them, but, in anger, Anita says that Chino, jealous of Maria's love for Tony, shot her dead. When Doc informs Tony, who is hiding in the cellar, of Maria's presumed death, Tony goes out to the street, yelling for Chino to kill him, too. When he arrives at the playground, Tony sees Maria, alive, and runs toward her, but Chino steps out of the shadows and shoots him. Tony falls into Maria's arms and as he dies, he and Maria talk about the place of which they had dreamed. Members of both gangs are gathering, and as they edge toward each other menacingly, Maria steps between them and takes the gun from Chino. Threatening both gangs with the gun, she accuses all of them of killing Tony, Riff and Bernardo. When Schrank and Krupke arrive, Maria kisses Tony and after she says "Te adoro, Anton," members of the two gangs, united at least for a while, help to carry Tony's body away.