WhenSpamAttacks.com writes: "Library Wars is a light novel series by Hiro Arikawa that was adapted into a manga by Kiiro Yumi in 2007. There were two manga adaptations, one aimed at shojo audiences and another at shonen. Viz Media picked up the shojo title and began releasing English volumes in June of this year. An 12 episode anime was released in 2008 that was followed by an OVA later that same year.
The premise for the story is that Japanese government passed the Media Betterment Act that allows the government to ban any media determined to be harmful society, with agents going out and confiscating books, etc. Local governments set up a counter agency to combat the MBA, that are essentially para-military forces through the libraries, to protect information and to keep things from being taken by the government. Hence the Library Defense Force."