If you walked into a library or bookstore last week, you might have seen a display of disparate books with one thing in common: Somebody, somewhere in the United States, wanted them removed from library shelves.

Banned Books Week, sponsored by the American Library Association -- the oldest and largest library association in the world -- and other organizations, is held each year to draw attention to books chosen by librarians for children to read that have been criticized.

In 2004, the last year for which statistics are available, the associations received 547 challenges -- formal, written complaints filed with a library or school requesting that materials be removed because of content. (A year earlier, 458 formal challenges were made.) Most books were not removed from shelves.

Staff writer Valerie Strauss interviewed Michael Gorman, association president and dean of library services at California State University at Fresno:

Q How do you account for a rise in the number of challenges in recent years?

A We have noticed more challenges to gay-themed books in school and public libraries. I wonder if that has to do with the prominence of issues such as same-sex marriage [and] civil unions and a consequent backlash.

Who is trying to remove books from library shelves?

Parents who think that your children should not read books of which they disapprove; organized groups with particular religious, moral or social opinions; and individuals or groups who recognize the power of books and reading and are afraid of it.

Clearly there are books that children are not mature enough to read. Is there a standard for school libraries?

School library books and other materials are selected by professional librarians skilled in selection of age-appropriate materials, sometimes within guidelines drawn up by boards.

Where is the line?

A good and complex question and one that is very much dependent on the context. Children should be encouraged to inquire and to seek knowledge, not deterred.

Most frequently challenged books in 2004:

1. "The Chocolate War," by Robert Cormier, for sexual content, offensive language, religious viewpoint, being unsuited to age group and violence.

2. "Fallen Angels," by Walter Dean Myers, for racism, offensive language and violence.

3. "Arming America: The Origins of a National Gun Culture," by Michael A. Bellesiles, for inaccuracy and political viewpoint.

4. Captain Underpants series by Dav Pilkey, for offensive language and modeling bad behavior.

5. "The Perks of Being a Wallflower," by Stephen Chbosky, for homosexuality, sexual content and offensive language.

6. "What My Mother Doesn't Know," by Sonya Sones, for sexual content and offensive language.

7. "In the Night Kitchen," by Maurice Sendak, for nudity and offensive language.

8. "King & King," by Linda de Haan and Stern Nijland, for homosexuality.

9. "I Know Why the Caged Bird Sings," by Maya Angelou, for racism, homosexuality, sexual content, offensive language and unsuitability to age group.

10. "Of Mice and Men," by John Steinbeck, for racism, offensive language and violence.

(This year marks the first in five in which the Harry Potter series does appear on the annual list.)