Here are four movies you may not have known were based on books.

1. Bridget Jones’s Diary

The romantic comedy Bridget Jones’s Diary (2001) is based on the novel of the same name, written by Helen Fielding.

In the movie adaptation, Renée Zellweger plays Bridget, a woman struggling with her self-worth, love life, and everything in between. Determined to get her life on track and finally find true love, Bridget starts her journey on New Year’s Day and chronicles her pursuits in a personal diary. Eventually, Bridget starts a romance with her boss Daniel Cleaver (Hugh Grant). Bridget also keeps running into the attractive but surly and pretentious Mark Darcy (Colin Firth). It’s a classic 2000s romantic comedy.

2. Forrest Gump

While the Oscar-winning Forrest Gump is one of the most successful, well-known films ever, what is not well-known about this movie is that it’s actually based on a novel written by Winston Groom. The book actually didn’t get much attention until its film adaptation.

3. Mean Girls

Mean Girls is based on the book Queen Bees and Wannabes by Rosalind Wiseman, a self-help books for parents with teenage daughters. The screenplay for the teen comedy was written by SNL alum Tina Fey. Since its 2004 release, Mean Girls has become a cult classic and one of the most quotable movies ever.

4. Pitch Perfect

Pitch Perfect (2012) is actually based on the non-fiction book Pitch Perfect: The Quest for Collegiate A Cappella Glory. Written by Mickey Rapkin, a senior editor at GQ, the book is based on Rapkin’s season following collegiate a cappella groups around the U.S.