Throughout history, the focus of censorship has fluctuated from generation to generation. Books and other materials have not been selected or have been removed from library collections for many reasons, among which are prejudicial language and ideas, political content, economic theory, social philosophies religious beliefs, sexual forms of expression, and other topics of a potentially controversial nature.
Labeling is the practice of describing or designating certain library materials by affixing a prejudicial label to them or segregating them by a prejudicial system. The American Library Association opposes this as a means of predisposing people's attitudes towards library materials for the following reasons:
The American Library Association declares as a matter of firm principle that it is the responsibility of every library to have a clearly defined materials selection policy in written form which reflects the Library Bill of Rights, and which is approved by the appropriate governing authority.
Some library procedures and practices effectively deny minors access to certain services and materials available to adults. Such procedures and practices are not in accord with the Library Bill of Rights and are opposed by the American Library Association.
Restricting access of certain titles and classes of library materials is a practice common to many libraries in the United States. Collections of these materials are referred to by a variety of names such as "closed shelf," "locked case," "adults only," or "restricted shelf."
Three reasons generally advanced to justify restricted access are:
