Many of the most popular movies being released today are actually adaptations. Blockbuster hits like The Hunger Games, The Lord of the Rings and the Harry Potter series are all adapted from popular book series. The Amazing Spiderman and all of the X-Men movies were originally comics. Jersey Boys and August: Osage County saw their beginnings on Broadway. Even many beloved Disney movies come from fairy tales – but we knew that already.

While movies that are adaptations usually name the source in the credits, many people don’t pay attention to this and leave the theater blissfully unaware. So how many movies in the following list will surprise you? Take a look.

How to Train Your Dragon/How to Train Your Dragon 2

Dreamworks’ How to Train Your Dragon series – which includes two movies, a TV show, three short films, and another sequel in the future – gained popularity with its endearingly dorky protagonist, Hiccup, and his dragon, Toothless. Many fans are unaware that the series’ origin comes from Cressida Cowell’s children’s books. Cowell’s How to Train Your Dragon was originally published in 2003 and, to date, has 12 total books in the series. The books are pretty funny and feature characters and stories that haven’t been used in the movies – at least not yet.

The Shawshank Redemption

The 1994 movie is has been critically acclaimed since its release and is on many people’s favorite movies list. Before it was a movie, The Shawshank Redemption was a novella titled Rita Hayworth and the Shawshank Redemption, written by Stephen King. The movie stays true to the novella with one major exception – the character Red, portrayed by Morgan Freeman in the movie, is actually a red-haired Irishman in King’s story.

Clueless

What do Clueless and Pride and Prejudice both have in common? They’re both movies that are based on Jane Austen books. Clueless is very loosely based on the book Emma. Austen’s story of a young woman trying to play matchmaker while finding love for herself translates well into the ‘90s Beverly Hill setting, proving that Austen’s stories are timeless.

Who Framed Roger Rabbit

Who Framed Roger Rabbit recently gained attention when its star, Bob Hoskins, passed away. The movie was innovative for its time, combining animation with live action. This movie is a much more light-hearted take on Who Censored Roger Rabbit?, written by Gary K. Wolf. The two stories do not share many similarities; Roger Rabbit is killed off and Eddie Valiant is in search of his killer. The author attempted to cash in on the film’s popularity with a sequel that attempted to retcon the events of the first book.

Howl’s Moving Castle

Hayao Miyazaki fans know that this movie is one of his best works, complete with gorgeous scenery shots – a Miyazaki staple – and charming characters. Sophie, a young woman, gets turned into an old lady when she unintentionally insults the Wicked Witch of the Waste. She ends up traveling with Howl, a wizard who steals young girls’ hearts, in his moving castle and gets caught up in his magical world. Miyazaki adapted his movie from Diana Wynne Jones’ book of the same title. While the first half of the film stays true to its source, the second half diverges into a different – but still enjoyable – storyline.

Shrek

Everyone’s favorite grumpy ogre made his first appearance in William Steig’s picture book Shrek! The original book tells the story of an ugly ogre who gets sent out into the world to scare and destroy. He ends up marrying an equally ugly princess and the two of them spend their days scaring anyone who annoyed them. The movie delves into the characters a bit more – though having three additional movies can help with that – and generally portray Shrek a bit more sympathetically.

Annie

You’d have to be living under a rock if you didn’t know that the film Annie was based on the musical of the same name. However, what fewer people know is that the musical was based on the 1920’s comic strip “Little Orphan Annie.” The comic featured many political undertones, especially after the stock market crash of 1929.

The Princess Bride

This cult classic has gained a huge and enthusiastic following since its initial release, due in no small part to its quotability. William Goldman, who wrote the screenplay, also wrote the novel The Princess Bride. The two mediums share the same storyline – the courtship, misadventures, and eventual wedding of Buttercup and Westley as they fight against the evil Prince Humperdinck’s plot – but the book makes full use of a rather entertaining narrative technique. Goldman writes it as an abridgement of a novel of the same name by fictional author S. Morgenstern. He even claims to have descended from a family in Florin – the fictional country featured in the book. The narrative is so well done that even people who know Florin is a fictional country find themselves wondering they can find the original copy of Morgenstern’s classic.

Scarface

You may well be aware that Brian de Palma’s 1983 film Scarface, starring Al Pacino in easily his most famous role, was based on an older movie of the same name. What you might not know is that the 1932 film was also an adaptation, this time of a novel by Maurice Coons. The book was inspired by none other than Al Capone himself, as well as the Sicilian organized crime scene in 1920’s Chicago. Various urban legends claim that Coons spent as long as two years on the streets of Chicago taking notes and collecting research. One only hopes that he wasn’t in as desperate need of rehab as Tony Montana by the time he found what he was looking for.

Psycho

We’re not going to talk about the 1998 remake; Hitchcock’s 1960 film of the same name is still the gold standard when it comes to psychologically devastating horror movies. Hitchcock broke new ground by killing off his female lead barely a third of the way into the film (sorry for the spoilers, but it’s been out for more than 50 years!). What many viewers don’t know is that Hitchcock shares credit for this disturbing film with Robert Bloch, who wrote the book it’s based on.