The American Library Association (ALA) promotes the freedom to choose or the freedom to express one's opinions even if that opinion might be considered unorthodox or unpopular and stresses the importance of ensuring the availability of those viewpoints to all who wish to read them. 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. As such, they are a threat to freedom of speech and choice. The ALA Office for Intellectual Freedom (OIF) promotes awareness of challenges to library materials and celebrates freedom of speech during Banned Books Week. This event is typically observed during the last week of September of each year.