Sunday marked the start of Banned Books Week, a celebration of freedom, and a recognition of the threat of censorship. Libraries around the US are hosting events.

Books are banned for a variety of reasons, and by a variety of organizations. Although mostly, its about sex.

Sherman Alexie and John Green are both frequently banned, but its Dav Pilkey’s Captain Underpants that has been most frequently banned in recent years.

Some organizations have suggested alternative solutions like content ratings, but even ratings lead to censorship. That’s also one of the dangers that come along with trigger warnings.

Arizona has even gone as far as banning entire curriculums, eliminating Mexican American Studies including Chicano literature like The House On Mango Street, Bless Me, Ultima, and The Magic of Blood.

And if you’re thinking that Fahrenheit 451 could never happen in the United States, remember, it already has.