The American Library Association (ALA) estimates that only 20-25% of book challenges (formal requests that library materials be removed or restricted) are reported to their office each year. Some libraries report challenges and some do not. In order to get more accurate data on what books are challenged, where, and how often, the ALA is encouraging everyone, not just librarians, to report any challenges they know of to its Office of Intellectual Freedom. Reports to the ALA will be confidential and may be made anonymously. An online reporting form is available here, or may be filled out in hard copy using this form.
For more information about banned or challenged books see my Banned Books Week website, or my Banned Books Week MaxGuide.
Read the Library Bill of Rights for more information about the role libraries play in protecting the rights of all to have access to information.