It’s Banned Books Week, an annual celebration of the freedom to read, sponsored by the American Library Association. Every year, libraries and bookstores around the country use the week to highlight censorship by displaying books that are challenged and/or banned, and hosting events about the issue. 

More than 11,300 books have been challenged in libraries and schools since 1982, when Banned Books Week began. The 10 most challenged books in 2012 were:

1. Captain Underpants (series), by Dav Pilkey
   Reasons: Offensive language, unsuited for age group
2. The Absolutely True Diary of a Part-Time Indian, by Sherman Alexie
   Reasons: Offensive language, racism, sexually explicit, unsuited for age group
3. Thirteen Reasons Why, by Jay Asher
   Reasons: Drugs/alcohol/smoking, sexually explicit, suicide, unsuited for age group
4. Fifty Shades of Grey, by E. L. James.
   Reasons: Offensive language, sexually explicit
5. And Tango Makes Three, by Peter Parnell and Justin Richardson.
   Reasons: Homosexuality, unsuited for age group
6. The Kite Runner, by Khaled Hosseini.
   Reasons: Homosexuality, offensive language, religious viewpoint, sexually explicit
7. Looking for Alaska, by John Green.
   Reasons: Offensive language, sexually explicit, unsuited for age group
8. Scary Stories (series), by Alvin Schwartz
   Reasons: Unsuited for age group, violence
9. The Glass Castle, by Jeanette Walls
   Reasons: Offensive language, sexually explicit
10. Beloved, by Toni Morrison
    Reasons: Sexually explicit, religious viewpoint, violence

You can find lists of frequently challenged books in earlier years here.