Books are commonly censored or banned from libraries for various reasons such as containing inappropriate content, challenging beliefs, or being deemed unsuitable for certain age groups. According to the document, while the library industry promotes free access to information, books are still removed due to complaints or to conform to community standards. Some of the most challenged books in the US deal with topics such as sexuality, violence, and religious or political viewpoints. The document discusses how censorship can prevent access to important ideas and knowledge, and provides quotes from teens who believe banned books can offer valuable perspectives. It suggests ways to help prevent censorship such as organizing reading groups or petitions to keep challenged books available.