Description: The International Standard Book Number is a numeric commercial book identifier which is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency.An ISBN is assigned to each edition and variation of a book. For example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, and 10 digits long if assigned before 2007. The method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967, based upon the 9-digit Standard Book Numbering created in 1966. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO 2108 . Privately published books sometimes appear without an ISBN. The International ISBN agency sometimes assigns such books ISBNs on its own initiative.Another identifier, the International Standard Serial Number , identifies periodical publications such as magazines; and the International Standard Music Number covers for musical scores.