Book banning: a silly thing that's still happening! Especially in schools. This week, the American Library Association is celebrating Banned Books Week (you can join in by reading a banned book) for the 31st year in a row. And Captain Underpants by Dav Pilkey tops the list of the most-challenged books in 2012. 

The Captain Underpants series has been around since 1997, but it's made quite the resurgence on the most-challenged list this year. Rounding out the top three are The Absolutely True Diary of a Part-Time Indian by Sherman Alexie (a National Book Award winner) and Thirteen Reasons Why by Jay Asher, which deals with teen suicide. All three books are meant for young adults. ALA President Barbara Stripling told The Guardian

Young adult is a big trend right now, and a high number of complaints are directed at those books. here is a lot of pressure to keep teenagers safe and protected, especially in urban areas, and we are seeing many more complaints about alcohol, smoking, suicide and sexually explicit material.

The fourth most-challenged book was the somewhat less surprising Fifty Shades of Grey. To be clear, schools aren't stocking that one in their libraries — E.L. James's Twilight fanfic made it to the list because people were complaining to their local libraries that carried it.