A popular novel by Mary Rodgers. A teenage girl called Annabel Andrews argues with her mother over whose life is easier and subsequently wakes up in her mother's body. Annabel quickly finds out that being an adult isn't as easy as it looks.
It has been made into three movies in 1976, 1995, and 2003 and was followed by another novel, A Billion For Boris
- Adult Fear: Near the end of the book, Annabel comes home to find that Boris let her brother go out with a girl he didn't recognize. It turns out to be her, without her braces and with pretty clothes.
- Annoying Younger Sibling: Annabel doesn't like her brother, thinking that he's trying to show her up. But after spending some time together, she discovers he really likes her and she comes to like him better.
- Be Careful What You Wish For: Annabel wishes she could be her own boss. She soon is, but finds that there are a lot of things to be considered.
- Brilliant but Lazy: Annabel's English teacher explains to Annabel/Mrs. Andrews that part of their hostile relationship is because of her frustration with her very bright student's unwillingness to apply herself.
- "Freaky Friday" Flip: The Trope Namer. Annabel somehow gets body-swapped with her mother.
- Freudian Slip: Played With. When the school psychologist asks "Mrs. Andrews" about her relationship with her husband, Annabel says that "it's none of your business about my relationship with my father!" The reader knows why she said it, but the psychologist takes it as a "revealing" slip.
- I Want My Mommy: After spending a day in her mother's body, Anabelle has no idea where her own body has gone to, where her little brother is, or what happened to her mother's personality (she doesn't know for sure if her mom is in her own body). After trying very hard to stay calm and figure it all out, she finally breaks down and calls out "Mom? Mom? MOMMY!" Fortunately Anabelle's mother, who was in her daughter's body and had been out with her little brother the whole time, came home just in time. Hearing an adult scream "Mommy!" clued her in that Anabelle learned the intended lesson of some of the less pleasant things that come with an adult life, like Adult Fear.
- Malicious Misnaming: Annabel calls her brother "Ape Face" to annoy him. It turns out that he likes it, and doesn't tell her because then she'd stop calling him it.
- Must Have Caffeine: Annabel's mother needs her coffee, and gets grouchy when told she can't have it because it will stunt her growth.
- Skipping School: Annabel's mother plays hooky and spends the day going to the dentist to get Annabel's braces taken off and buying clothes for her daughter.
- Trash of the Titans: Annabel's room is so messy the cleaning lady refuses to touch it.
- The Unreveal: Neither the reader nor Annabel ever find out how her mother accomplished the body-swap.
- You Have to Believe Me: Annabel starts, well, freaking out for a variety of reasons, one of which being that while she is inhabiting her mother's body, her mother has presumably gone joyriding in hers, and is now nowhere to be found. She decides to call the police. Instead of saying, "I'm deeply concerned that my daughter has vanished", she decides to blurt out the whole body-swapping story. The cops, unsurprisingly, think she's nuts.