In early autumn, after three separate pregnancy tests confirm positive results, sixteen-year-old Minnesota punk music aficionado Juno MacGuff accepts that she is pregnant after a single sexual experience on an easy chair with her friend, Paulie Bleeker. Returning home from the convenience store after taking the final test, Juno calls her best friend Leah on her telephone that looks like a hamburger and has some difficulty in convincing Leah of the seriousness of her situation. The next morning, Juno greets Paulie outside his home as he is about to join up with the Dancing Elk track team, of which he is a member. In her characteristically sardonic manner, Juno reveals that she is pregnant and, although stunned, Paulie asks her what they should do. Juno announces that she will "nip it in the bud" and heads off to school for the day. That afternoon, Juno telephones Women Now to arrange for an abortion. Upon arriving at the clinic later, Juno is surprised to run into Su-Chin, a classmate who is picketing against abortion. After Su-Chin fervently advises Juno against going through with her plans, insisting that the fetus has feelings and fingernails, Juno goes inside the clinic where she is unexpectedly disconcerted by the receptionist’s offer of a flavored condom. Further unsettled by the other people waiting at the clinic, Juno bolts, going to Leah to confess that she has decided to have the baby and give it up to some unfortunate couple who cannot conceive or a lesbian couple. Leah excitedly suggests perusing the local Penny Saver for ads by hopeful adopters and although Juno scoffs, insisting that she wants the child to have cool parents, the girls soon find an advertisement placed by Mark and Vanessa Loring, a well-to-do suburban couple. That evening, with Leah on hand for moral support, Juno informs her father Mac and stepmother Brenda about her condition, but hastily explains that she has found a potentially ideal couple to adopt. Taken aback, Mac and Bren nevertheless offer to help Juno, with Mac insisting on accompanying her to the meeting with the Lorings. A day later, Juno and Mac travel about an hour away to the Lorings' large, comfortable home where their attorney, Gerta Rauss, oversees the discussion. After Juno reveals that she is twelve weeks pregnant and expects to deliver in May, Vanessa explains that the couple is more than willing to conduct an open adoption, which means that Juno will receive regular updates on the child’s progress. Startled, Juno insists on an old-fashioned, closed adoption so she will have no contact with the child. Vanessa and Mark propose to pay for all of Juno’s medical expenses and when they warily inquire if she expects further remuneration, she hotly refuses. Later, after visiting the upstairs bathroom, Juno is distracted by Vanessa’s abundant toiletries, then by a room filled with guitars and electrical musical equipment. Joining her, Mark admits he once belonged to a rock band and the two discuss various music groups. When they begin singing together, however, an exasperated Vanessa intervenes. Mark explains that his wife is anxious about Juno, because the couple had tried to adopt before and the mother had reneged at the last minute. Assuring the Lorings that she is “104 percent” sure she will give up the baby, Juno departs with Mac. In winter, as Juno’s pregnancy becomes obvious, she comes under critical scrutiny at school by both students and staff. At her ultrasound exam, though Juno tries to remain detached, she is pleased at the results but asks not to know the baby's gender so as to surprise Vanessa and Mark upon its birth. When the technician makes disparaging remarks about the irresponsibility of teen pregnancies, Bren angrily tells her off as Leah and Juno look on approvingly. On impulse, Juno drives out to the Lorings' to present them with the ultrasound scan, but finds Mark alone as Vanessa is working late. Mark reveals that he works mostly from home as a composer of advertising jingles. Upon comparing favorite horror movies with Juno, Mark puts on his favorite slasher film, which ends as Vanessa arrives home bearing numerous baby items. When Juno tells Vanessa that she should wait for all the presents she will receive at the baby shower, Vanessa admits that she does not feel she can have a shower because she continues to fear that Juno will get cold feet about the adoption. Later, at home after Juno tells Bren of her visit to the Lorings, her stepmother cautions her about intruding upon a married couple’s dynamics, but Juno dismisses her concern. Risking the disapproval of Mrs. Bleeker, Juno visits Paulie at home and they reminisce about their time together in a punk band. Admitting they have always enjoyed each other’s company, Paulie suggests they resume their romantic relationship but Juno remains evasive and suggests he see other girls. At the Lorings', Vanessa asks Mark his opinion about the paint color for the nursery, but he insists it is too soon to make such decisions. A few days later at the mall, Juno and Leah see Vanessa shopping with some of her friends and their children, and Juno is struck by how loving Vanessa is with the children. Greeting her moments later, Juno describes how odd it feels when the baby kicks. Shyly asking if she may touch Juno’s stomach, Vanessa hopes to feel the baby move. When initially there is no movement, Juno suggests that Vanessa speak to the baby in encouragement, and she is soon rewarded by the baby’s kick. In spring, the very pregnant Juno telephones Mark to thank him for a recent music disc he made for her. Upon learning from Leah that Paulie is taking a fellow classmate to the prom, Juno is unexpectedly jealous and upset, even though she knows that Paulie does not like the girl. Confronting him later, Juno accuses Paulie of hypocrisy and ignores his insistence that he and the girl are only friends. Annoyed, Juno drives to the Lorings' to deliver some music discs to Mark. Delighted by Mark’s gift of a Japanese comic book about a pregnant superhero, Juno relates that Mac named her after the Roman goddess Juno, the wife of the powerful Zeus. Upon listening to a slow song, Mark dances with Juno, then after a few moments, confesses that he is going to leave Vanessa. When Juno responds angrily, Mark demands to know why she visits constantly. Bewildered, Juno says she wants to feel a part of the people who want her baby, then pleads with Mark to stay with Vanessa to raise the baby. Regretfully, Mark professes that he is no longer in love with his wife and not yet ready to have a child. Upon Vanessa’s arrival moments later, Mark reveals his doubts and Vanessa insists he must grow up and accept that he will never be a rock star. Deeply distressed, Juno leaves the house and cries as she drives away. Later that same evening, after Mark contacts Gerta to start divorce proceedings, Juno leaves a note for Vanessa on the doormat. Back home, Juno confides in Mac that her faith in human nature has been deeply shaken and asks if couples really can remain devoted to each other and in love. Mac acknowledges that it is very difficult, but maintains that people who truly love someone despite their flaws tend to remain together. Pleased, Juno visits Paulie’s house the next day and leaves him a large supply of his favorite orange-flavored breath mints. Later, when the two meet at the track field, Juno confesses that she is in love with him because he is cool without trying, to which he shyly replies that he tries very hard. A few days later, when Juno goes into labor, Mac, Bren and little sister Liberty Bell rush her to the hospital. Although Juno does not contact Paulie because he has an important track meet, after winning and not seeing Juno in the bleachers, Paulie rushes to the hospital. He agrees with Juno's decision not to see the baby, a boy, then climbs into bed and comforts her while she gently sobs. As Juno had hoped and indicated in the note she left on the Lorings' doormat, Vanessa adopts the baby on her own. A few months later, Juno has returned to her life as a teenage student and to seeing and singing with Paulie, whom Juno regards as the best boyfriend ever.