The American Library Association (ALA) defines a challenge to literature as an attempt by a person or group of people to have literature restricted or removed from a public library or school curriculum. Merely objecting to material is not a challenge without the attempt to remove or restrict access to those materials. The ALA defines a challenge thus:
A challenge is an attempt to remove or restrict materials, based upon the objections of a person or group. A banning is the removal of those materials. Challenges do not simply involve a person expressing a point of view; rather, they are an attempt to remove material from the curriculum or library, thereby restricting the access of others.
According to the ALA, a successful challenge would result in removal of those materials, a form of censorship. However, the ALA agrees that materials may be removed from libraries in appropriate circumstances and Island Trees School District v. Pico suggested that books that are pervasively vulgar may be removed legally.
Challenges in the U.S. and Canada—tracked by the Canadian Library Association's Advisory Committee on Intellectual Freedom, and the Book and Periodical Council's Freedom of Expression Committee—are often brought by parents wishing to prevent their children from having access to content that they deem to be inappropriate or offensive. The ALA suggests that, while parents and guardians should have the right to determine their children's access to library resources, that right applies only to their children and no library policy, such as restrictive scheduling or usage policies, should deny children access to library resources.
The differences between challenging a book and banning were discussed by a columnist for American Decency who raised concerns that "efforts by parents to become involved in their children's education by raising questions concerning age-appropriate material" was being referred to as banning. Similarly, former ALA Councilor Jessamyn West said, "The bulk of these books are challenged by parents for being age-inappropriate for children. While I think this is still a formidable thing for librarians to deal with, it's totally different from people trying to block a book from being sold at all."
The ALA believes that it is important to monitor challenges made to books as well as actual bannings since a challenge may lead to self-censorship by those seeking to avoid controversy.