An International Standard Book Number, or ISBN, does not provide copyright protection. Rather, an ISBN is a unique 13-digit number universally used to identify books for marketing purposes for international book trade. Copyright protection is administered by the Library of Congress.
ISBNs are assigned for a price by private companies at the request of a publisher, and each publisher is issued a unique publisher prefix, or "root." When printed, the 13 digits of an ISBN are preceded by the letters ISBN. The exclusive ISBN-issuing agent in the United States is R.R. Bowker, which issued approximately 2.35 million ISBNs in 2012. A book's bar code is a visual representation of the ISBN.