Censorship is a practice that limits public access to materials, including printed text, photographs and art, music and video, or other multimedia, based on the value judgments or prejudices of the censoring individuals or groups. According to psychologist Sara Fine, censorship is essentially a defense mechanism triggered by fear of threats of some sort. Whether this fear is based on a real threat, an exaggeration of some actual danger, or an unconscious reaction to some dark, hidden impulse is irrelevant. Thus, just about any material can be censored. Materials most likely to be censored in the United States are those that deal with sex and sexuality, challenge the authority of adults, or differ from the censor's beliefs and traditions.

Librarian Lester Asheim points out that censorship is different from selection, which is the process of deciding which resources to include in a museum or...