Juno is a sixteen year old high student faced with an unexpected . The father is another teenager , Paulie Bleeker, 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 of the situation.

She enlists the help of her best friend Leah. She considers Woman's Help Center for what she calls "Speedy Abortion", but her friend Su-Chin, an anti-abortion , tells her just outside the clinic that the fetus probably has fingernails by now and Juno changes her . Together she and Leah find an ad in the local newspaper from Mark & Vanessa Loring, who are for a child.

Facing her parents is a different story all together. After announcing she has bad , there is a short but awkward guessing game as her dad, Mac Macguff, and her stepmother, Bren Macguff ironically conclude they would have rather heard that she might be into drugs. They decide to her through the pregnancy. Her dad meets the Lorings' lawyer close an agreement. Although the Lorings are willing to have an open adoption, Juno prefers a closed

Through the pregnancy Juno starts to appreciate her imperfect . On the other hand, the Lorings, who look perfect from the outside, have within. Vanessa, although desperately wanting to be a mom, is reserved since she's been hurt in a prior adoption attempt. Mark is a musician turned composer for TV commercials. His love for 80s music and slasher movies is shared by Juno. Keeping her parents conveniently unaware of her comings and goings, Juno starts driving over to see Mark while Vanessa is at work, and as they their interests in music and movie gore, he realizes he isn't ready for a child, and he confides in Juno that his with Vanessa is going through difficult times, and he has things he still wants to do.

A lot of questions burst out in Juno’s mind:
Will Mark and Vanessa adopt her baby? Will she find the of her life and be happy in the end? These questions will find an answer as the due arrives. Some of them will be really surprising.