Hollywood often turns to novels and non-fiction books for movie ideas, but sometimes the films are so popular that they overshadow their source material. Here are 20 famous movies you might not know were based on books. [Note: Some spoilers.]

1. Movie: Die Hard // Book: Nothing Lasts Forever

Author Roderick Thorp wrote Nothing Lasts Forever after watching The Towering Inferno, which features a skyscraper that catches on fire. Thorp envisioned a group of terrorists with guns chasing his character Joe Leland, a retired NYPD detective, through the skyscraper’s fiery ash. Nothing Lasts Forever was later adapted into Die Hard with the main character’s name changing from Joe Leland to John McClane.

Both stories feature NYPD detectives in the middle of a terrorist siege inside of a skyscraper on Christmas Eve in Los Angeles, but a notable difference is that Die Hard features a young version of the main character and a different ending. While Die Hard includes a happy ending, Nothing Lasts Forever ends with Leland’s life in the balance.

2. Movie: The Parent Trap // Book: Lottie and Lisa (Das Doppelte Lottchen)

Disney’s original Parent Trap starring Hayley Mills was based on a German novel titled Lottie and Lisa (Das doppelte Lottchen) from author Erich Kästner. The novel was first published in 1949 and was turned into various film and TV adaptations from nine countries, including the United States, Germany, India, Japan, and Iran.

3. Movie: Rambo: First Blood // Book: First Blood

Author David Morrell sold the film rights to his novel First Blood in 1972, shortly after it was published. But the property went through an extensive development period; there were various iterations of the screenplay because of its subject matter and themes surrounding the Vietnam War.

The main difference between the book and the movie is its ending. The character John Rambo commits suicide at the end of the book, while he turns himself in to the authorities in the film.

4. Movie: Who Framed Roger Rabbit // Book: Who Censored Roger Rabbit?

The Walt Disney Company acquired the rights to Gary K. Wolf’s 1981 book Who Censored Roger Rabbit? Frank Marshall, Kathleen Kennedy, and Steven Spielberg developed the project and convinced rival studios to loan Disney their iconic cartoon characters, such as Warner Bros’ Bugs Bunny and Daffy Duck.

The novel was presented as a hardboiled spoof that took place during modern times and featured the death of Roger Rabbit, a cartoon character on the downswing of his career, while Who Framed Roger Rabbit? was family friendly and lighter in tone.

5. Movie: Full Metal Jacket // Book: The Short-Timers

In 1987, Stanley Kubrick adapted Marine Corps veteran Gustav Hasford’s 1979 novel The Short-Timers into Full Metal Jacket. While both feature soldiers going from boot camp to the Vietnam War front, Stanley Kubrick’s film re-arranges the novel’s structure into something more cohesive and tragic in tone.

6. Movie: Mean Girls // Book: Queen Bees and Wannabes: Helping Your Daughter Survive Cliques, Gossip, Boyfriends & Other Realities of Adolescence

In 2004, Tina Fey called upon Saturday Night Live creator Lorne Michaels to produce a film version of Rosalind Wiseman’s book Queen Bees and Wannabes, and Michaels got in touch with Paramount Pictures to acquire the film rights. Although Queen Bees and Wannabes is non-fiction, Fey incorporated elements of her own high school experience into the screenplay.

7. Movie: There Will Be Blood // Book: Oil!

Paul Thomas Anderson’s Academy Award-winning There Will Be Blood was a loose adaptation of Upton Sinclair’s 1927 novel Oil! While Anderson was a big fan of the original source material, he only adapted the novel’s first 150 pages to There Will Be Blood. He decided to take the story in a different direction, focusing on the self-made oil tycoon Daniel Plainview, played by Daniel Day-Lewis, rather than the character's son.

8. Movie: Mrs. Doubtfire // Book: Alias Madame Doubtfire

The 1993 hit comedy Mrs. Doubtfire is based on British author Anne Fine’s young adult novel titled Alias Madame Doubtfire. The movie and the book share very similar plots: Both feature a man, who — after a messy divorce that limits his time with his family — dresses like an old woman to take a job as his kids' nanny.

9. Movie: Pitch Perfect // Book: Pitch Perfect: The Quest for Collegiate A Cappella Glory

Former GQ editor Mickey Rapkin spent an entire season covering competitive collegiate a cappella at Tufts University, the University of Oregon, and the University of Virginia for his non-fiction book, which screenwriter Kay Cannon adapted into the comedy Pitch Perfect. The film was a sleeper hit, taking in a $113 million worldwide box office haul in 2012.

10. Movie: Drive // Book: Drive

In 2005, producers Marc E. Platt and Adam Siegel acquired the film rights to James Sallis’ Drive shortly after Siegel read a rave review of the novel. The producers originally wanted Drive to be an action thriller with Hugh Jackman in the starring role as The Driver. Ultimately, Jackman dropped out of the project, Ryan Gosling signed on to play the lead, and the film transformed into a character drama.

11. Movie: The Town // Book: Prince of Thieves

Although director Adrian Lyne and producer Graham King bought the film rights to Chuck Hogan’s Prince of Thieves, which followed a team of bank robbers planning one last heist, they were unable to adapt the novel to Warner Bros’ requirements for a two-hour movie with a budget under $37 million. However, Ben Affleck, fresh off his directorial debut Gone Baby Gone, signed on to the project to star, write, and direct the film adaptation, which was re-titled The Town.

12. Movie: Clueless // Book: Emma

Amy Heckerling’s teen comedy Clueless is a modern film adaptation of Jane Austen’s 1815 novel Emma. Clueless launched the careers of its young cast — including Alicia Silverstone, Britney Murphy, Donald Faison, and Paul Rudd.

13. Movie: Cruel Intentions // Book: Les Liaisons dangereuses (The Dangerous Liaisons)

French author Pierre Choderlos de Laclos’ Les Liaisons dangereuses (The Dangerous Liaisons) serves as the inspiration for Cruel Intentions. The teen drama’s screenwriter/director Roger Kumble moved the story from the 18th century to the modern day, and instead of featuring French aristocrats, he made his characters wealthy and privileged teenagers living in New York City.

14. Movie: Slumdog Millionaire // Book: Q & A

The Academy Award winning Slumdog Millionaire was based on Indian author Vikas Swarup’s Q & A, which was first published in 2005. The novel followed a young orphan who becomes a very successful game show winner, only to be sent to jail under accusations of cheating.

15. Movie: Death Wish // Book: Death Wish

Death Wish was based on author Brian Garfield’s 1972 book of the same name, with considerable differences between the film and the novel. Both feature a man fed up with violent crime in New York City after the murder of his wife and the sexual assault of his daughter, but the film seems to enthusiastically support vigilante violence; the novel denounces it.

16. Movie: The Thing // Book: Who Goes There?

John Carpenter’s The Thing was based on the science fiction novella Who Goes There? by John W. Campbell, Jr., who wrote it under the pen name Don A. Stuart. The novella first appeared in the magazine Astounding Science-Fiction, published in August 1938.

17. Movie: Fast Times at Ridgemont High // Book: Fast Times at Ridgemont High: A True Story

Cameron Crowe, then 22, wrote Fast Times at Ridgemont High: A True Story, which chronicled his experience posing as a high school senior at Clairemont High School in San Diego, California. Amy Heckerling directed the film adaptation in 1982.

18. Movie: Silver Linings Playbook // Book: The Silver Linings Playbook

The Weinstein Company optioned author Matthew Quick’s debut The Silver Linings Playbook for a big screen adaptation before the book was released in September 2008. Although Sydney Pollack developed the project, it was handed over to David O. Russell at the time of Pollack’s death earlier in the year.

19. Movie: The Iron Giant // Book: The Iron Man: A Children's Story in Five Nights

Brad Bird’s directorial debut The Iron Giant was based on Ted Hughes’ 1968 modern fairy tale The Iron Man: A Children's Story in Five Nights. Bird took a few liberties with Hughes’ story, including changing its setting from the British countryside during the 1960s to an American coastal town during the 1950s. According to Bird, the time period “presented a wholesome surface, yet beneath the wholesome surface was this incredible paranoia. We were all going to die in a freak-out."

After its release, The Iron Giant won an Annie Award for Best Animated Feature Film in 1999.

20. Movie: Psycho // Book: Psycho

Alfred Hitchcock acquired the film rights to Robert Bloch’s horror genre novel Psycho for $9,500 in 1959. The director went as far as buying up every available copy in the country to keep the story’s surprises from the general public.

Although Psycho is one of Alfred Hitchcock’s most popular films, Paramount Pictures didn’t want the legendary director to make the movie because the studio felt its source material was objectionable and highly offensive. So Hitchcock put up his own money to help finance Psycho, used his Alfred Hitchcock Presents TV crew to make it, and agreed to shoot the film in black-and-white to keep production costs down.