Shutterstock

The American Library Association released its 2014 State of America's Libraries report in April, along with the 2013 list of the top 10 most frequently challenged books.

A "challenge," according to the ALA, "is defined as a formal, written complaint, filed with a library or school requesting that materials be removed because of content or appropriateness."

According to the ALA, there were 5,099 challenges reported to the Office for Intellectual Freedom from 2000 to 2009. Of these, 1,639 took place in school libraries, 1,811 were in classrooms, 1,217 were in public libraries, 114 were in college classes and 30 were in academic libraries, with the rest being made in places like prison or special libraries.

This is a look at the top 10 most frequently challenged books for 2013, along with a brief look at past challenges some of these same titles have faced:

12 Banned/challenged books from 1990-1999

Here's a look at the 10 books that led the ALA's top 100 banned/challenged books from 1990-1999 list:

1. "Scary Stories" (series), by Alvin Schwartz

2. "Daddy’s Roommate," by Michael Willhoite

3. "I Know Why the Caged Bird Sings," by Maya Angelou

4. "The Chocolate War," by Robert Cormier

5. "The Adventures of Huckleberry Finn," by Mark Twain

6. "Of Mice and Men," by John Steinbeck

7. "Forever," by Judy Blume

8. "Bridge to Terabithia," by Katherine Paterson

9. "Heather Has Two Mommies," by Leslea Newman

10. "The Catcher in the Rye," by J.D. Salinger

11 Banned/challenged books from 2000-2009

Here's a look at the 10 books that led the ALA's top 100 banned/challenged books from 2000-2009 list:

1. Harry Potter (series), by J.K. Rowling

2. Alice series, by Phyllis Reynolds Naylor

3. "The Chocolate War," by Robert Cormier

4. "And Tango Makes Three," by Justin Richardson/Peter Parnell

5. "Of Mice and Men," by John Steinbeck

6. "I Know Why the Caged Bird Sings," by Maya Angelou

7. "Scary Stories" (series), by Alvin Schwartz

8. "His Dark Materials" (series), by Philip Pullman

9. "ttyl; ttfn; l8r g8r" (series), by Lauren Myracle

10. "The Perks of Being a Wallflower," by Stephen Chbosky

10 Bone (series)

Title: Bone (series)

Author: Jeff Smith

Publishing date: 1991-2004

Synopsis: This comic book series follows the adventures of the three Bone cousins — Phoney Bone, Smiley Bone and Fone Bone.

Reasons for challenge: Political viewpoint, racism, violence

9 Bless Me Ultima

Title: Bless Me Ultima

Author: Rudolfo Anaya

Publishing date: 1972

Synopsis: This coming-of-age story focuses on Antonio Marez y Luna and his mentor, a curandera (woman folk healer) named Ultima.

Reasons for challenge: Occult/Satanism, offensive language, religious viewpoint, sexually explicit

Also listed (2000-2013):
No. 5 - 2008

No. 32 on the top 100 banned/challenged books: 2000-2009 list

8 The Perks of Being a Wallflower

Title: The Perks of Being a Wallflower

Author: Stephen Chbosky

Publishing date: The novel is written in letter format by Charlie, who is a wallflower, and tells of his experiences in high school as he is befriended by seniors Patrick and Samantha.

Synopsis: 1999

Reasons for challenge: Drugs/alcohol/smoking, homosexuality, sexually explicit, unsuited to age group

Also listed (2000-2013):
No. 3 - 2009
No. 6 - 2008
No. 10 - 2007
No. 8 - 2006
No. 5 - 2004

No. 10 on the top 100 banned/challenged books: 2000-2009 list

7 Looking for Alaska

Title: Looking for Alaska

Author: John Green

Publishing date: 2005

Synopsis: Character Miles Halter leaves home to attend an out-of-state school where he meets a complicated girl named Alaska.

Reasons for challenge:
Drugs/alcohol/smoking, sexually explicit, unsuited to age group

Also listed (2000-2013):
No. 7 - 2012

6 A Bad Boy Can Be Good for a Girl

Title: A Bad Boy Can Be Good for a Girl

Author: Tanya Lee Stone

Publishing date: 2006

Synopsis: Written in poetry format, "A Bad Boy Can Be Good for a Girl" tells of three girls who fall for the same bad boy and the experiences that follow.

Reasons for challenge: Drugs/alcohol/smoking, nudity, offensive language, sexually explicit

5 The Hunger Games

Title: The Hunger Games

Author: Suzanne Collins

Publishing date: 2008

Synopsis: Katniss Everdeen volunteers to participate in the yearly Hunger Games where 24 youths ages 12-18 battle to the death.

Reasons for challenge: Religious viewpoint, unsuited to age group

Also listed (2000-2013):
No. 3 - 2011
No. 5 - 2010

4 Fifty Shades of Grey

Title: Fifty Shades of Grey

Author: E.L. James

Publishing date: 2011

Synopsis: Student Anastasia Steele and businessman Christian Grey enter into a physical relationship on his terms.

Reasons for challenge: Nudity, offensive language, religious viewpoint, sexually explicit, unsuited to age group

Also listed (2000-2013):
No. 4 - 2012

3 The Absolutely True Diary of a Part-Time Indian

Title: The Absolutely True Diary of a Part-Time Indian

Author: Sherman Alexie

Publishing date: 2007

Synopsis: Native American teen Arnold Spirit Jr. narrates the story of his life on the Spokane Indian Reservation and the repercussions of his decision to attend an all-white school off the reservation.

Reasons for challenge: Drugs/alcohol/smoking, offensive language, racism, sexually explicit, unsuited to age group

Also listed (2000-2013):
No. 2 - 2012
No. 5 - 2011
No. 2 - 2010

2 The Bluest Eye

Title: The Bluest Eye

Author: Toni Morrison

Publishing date: 1970

Synopsis: The story follows a young African-American girl named Pecola Breedlove who considers herself to be ugly and dreams of having white skin, blonde hair and blue eyes.

Reasons for challenge: Offensive language, sexually explicit, unsuited to age group, violence

Also listed (2000-2013):
No. 5 - 2006

No. 15 on the top 100 banned/challenged books: 2000-2009 list

1 Captain Underpants (series)

Title: Captain Underpants (series)

Author: Dav Pilkey

Publishing date: 1997-present

Synopsis: Fourth-graders Harold and George turn their school principal into a superhero called Captain Underpants; adventures follow.

Reasons for challenge: Offensive language, unsuited for age group, violence

Also listed (2000-2013):
No. 1 - 2012
No. 8 - 2005
No. 4 - 2004
No. 6 - 2002

No. 13 on the top 100 banned/challenged books: 2000-2009 list