Most people don't realize that the U.S. Copyright Office is a part of the Library of Congress.

The Copyright Office protects the rights of authors of books as well as those of creators of music, designs, sound recordings, films, and digital materials so that they may benefit from their work.

Article I of the U.S. Constitution gives Congress the power "to promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries. …" In 1870, the U.S. Copyright Office was established at the Library of Congress (this function had been handled by U.S. District Courts since 1790) to protect written works of authors. Over time, this has been expanded to include other types of works.

The copyright law has played a major role in making the Library of Congress the world's largest. That's because, generally, two copies of every published work must be deposited at the Library. About 500,000 works are registered annually, though the Library retains only about half the deposits for its own permanent collections. Some deposits are exchanged with other libraries; others are donated to schools and nonprofit institutions. Contrary to popular myth, the Library does not have a copy of every book published in the United States.