Juno (Ellen Page) is a sixteen year old high school student faced with an unexpected pregnancy. The father is another teenager who she doesn't consider to be her boyfriend. She wants it to go away like a bad dream, but she realizes she needs to take control of the situation. She enlists the help of her best friend Leah (Olivia Thirlby). She considers Woman's Help Center for what she calls "Speedy Abortion", but her friend Su-Chin, an anti-abortion protester, tells her just outside the clinic that the fetus probably has fingernails by now and Juno changes her mind. Together she and Leah find an ad in the Penny Saver from Mark & Vanessa Loring (Jason Bateman, Jennifer Garner), who are desperate for a child.
Facing her parents is a different story all together. After announcing she has bad news, there is a short but awkward guessing game as her dad, Mac Macguff (J.K. Simmons), and her stepmother, Bren Macguff (Allison Janney), ironically conclude they would have rather heard that she might be into drugs or DWI. They decide to help her through the pregnancy. Her dad meets the Lorings' attorney to draw up a consent form. Although the Lorings are willing to have an open adoption, Juno prefers a closed adoption.
Through the pregnancy Juno starts to appreciate her imperfect family. Her dad is an AC & plumbing contractor whose first wife (Juno's mom) left him. The stepmother, who works in a nail salon, strongly supports her stepdaughter. On the other hand, the Lorings, who look perfect from the outside, have divisions within. Vanessa, although desperately wanting to be a mom, is reserved since she's been hurt in a prior adoption attempt. Mark is unhappy that his wife doesn't think he adds enough household income, since he works from home and his contribution isn't major. He is a musician turned composer for TV commercials. His love for 80s music and slasher movies is shared by Juno. Keeping her parents conveniently out of the loop of her comings and goings, Juno starts driving over to see Mark while Vanessa is at work, and as they share their interests in music and movie gore, he realizes he isn't ready for a child, and he confides in Juno that his relationship with Vanessa is strained, and he has things he still wants to do. Vanessa and Mark go through divorce proceedings and the chances for Juno's baby to be adopted appear bleak. In a revealing but gut-wrenching conversation with her dad, Juno comes to understand relationships and makes a decision to seek out the love of the boy who got her pregnant, because she actually cares for him and he probably cares a lot for her. They become very close and Juno finds she actually loves him. They become a couple, Juno delivers the baby, and rather surprisingly Vanessa still makes the adoption, as a single parent. Juno and her lover elect to not see the child, and to let matters take their course. In closing scenes, life has returned to normal.
