Whanganui District Library is celebrating an unusual event over the next seven days - Banned Books Week.
The initiative was started by the America Library Association (ALA), which has been documenting attempts to ban books in libraries and schools around the world since 1990.
A challenge to a book is an attempt to remove or restrict materials based upon the objection of a person or group, while a ban is the total removal of those materials.
Whanganui District Library currently stocks 45 of the ALA's 100 most challenged and banned books between 2010 and 2019.
Learning and discovery librarian, Esther Newrick, said the books weren't held because they were on the list, it was because they were "classics".
Books can be challenged for any number of reasons, including religious objections, race, political viewpoints, sexual content, and offensive language.
"To Kill a Mockingbird was published in 1960, and it was still one of the most challenged books from 2010 to 2019," Newrick said.
"Often they're award-winning titles that have been turned into movies or TV series, like Catch 22, Lord of the Flies, and even Harry Potter."
Other books on the list include The Catcher in the Rye, Goosebumps, A Clockwork Orange, One Flew Over The Cuckoo's Nest, and The Holy Bible.
New Zealand author Ted Dawe had his novel Into The River challenged and banned for six weeks in 2015, after concerns were raised about depictions of underage sex.
It was the first time a book had been subject to an interim restriction order in New Zealand in 22 years.
Unsurprisingly, Mein Kampf by Adolf Hitler also made the top 100 list.
In 2018, the third most challenged book was the Captain Underpants series, because it was perceived as "encouraging disruptive behaviour".
Captain Underpants and the Sensational Saga of Sir-Stinks-A-Lot was also challenged for including a same-sex couple.
Whanganui District Library stocks both Mein Kampf and Sir-Stinks-A-Lot.
Fellow learning and discovery librarian, Rachel Smith, said interest in novels like Into The River only spiked after they had been restricted.
"As soon as it was challenged, everybody wanted to read it. We had to remove it from the shelves, though.
"Even staff weren't allowed to take it during that time."
Newrick said the Whanganui District Library did deal with customers who objected to books from time to time.
"They might even write 'disgusting' or 'bad language' in the book itself. Sometimes words will be scratched out too."
"Maybe they think they're doing a service to other customers," Smith said.
At the end of the day, it was up to the individual to decide if they wanted to continue with a book or not, Newrick said.
"People are welcome to their opinions, as long as those opinions aren't stopping others accessing stuff.
"The role of the library is to give equal access to everyone. It's not really our role to censor.
"These books are really important, because even if they're challenging to start with, they get us talking, stimulate conversation and change views."
Whanganui District Library will be hosting a quiz and other events to celebrate Banned Books Week (September 26-October 2).