Taken directly from Wikipedia page.
Banned Books Week is an annual awareness campaign that celebrates the freedom to read and draws attention to banned and challenged books. The campaign “stresses the importance of ensuring the availability of those unorthodox or unpopular viewpoints to all who wish to read them” and the requirement to keep material publicly available so that people can develop their own conclusions and opinions. Its goal is “to teach the importance of our First Amendment rights and the power of literature, and to draw attention to the danger that exists when restraints are imposed on the availability of information in a free society.”
Held during the last week of September since 1982, Banned Books Week not only encourages readers to examine banned and challenged literary works, but also promotes intellectual freedom in libraries, schools, and bookstores. Offering Banned Books Week kits, the American Library Association (ALA) sells posters, buttons, and bookmarks to celebrate the event. Many educational facilities also celebrate banned and challenged books during this week, often creating displays and programs around the awareness campaign. Additionally, various booksellers sponsor activities and events in support of Banned Books Week. Some retailers create window displays, while others go further, inviting authors of banned and challenged materials to come speak at their stores, as well as funding annual essay contests about freedom of expression.
The campaign was founded in 1982 by prominent First Amendment and library activist Judith Krug. It is sponsored by the American Library Association (ALA), the American Booksellers Association, American Booksellers Foundation for Free Expression (ABFFE), American Society of Journalists and Authors, Association of American Publishers, National Association of College Stores, and endorsed by the Center for the Book in the Library of Congress.