The ISBN number is usually located on the back cover of a book, next to the barcode. If the ISBN is not shown on the back cover of a book, look on the page that contains the copyright and publisher information; the ISBN will be located there. The ISBN is 13 digits long; it should begin with 978 or 979. There are also ISBN agencies which can help you obtain an ISBN for a book. These agencies check whether books they receive have existing ISBNs that they can loan out, instead of having to generate new numbers. Many libraries use ISBN agencies to obtain new numbers before they go into circulation. Agencies charge fees for their services. In addition to books, some magazines, newspapers, and academic journals include an ISSN (International Standard Serial Number). This is a nine-digit number used by publishers to identify their publications. It is found on the front cover of a magazine, alongside the editor's name and address. An ISSN must contain the letters "ISBN" followed by three numbers separated by dashes. For example, the ISSN for Books & Music Magazine is 07-8051-5105. An ISBN cannot be used once it has been used by another publication. If this happens, the only option is to regenerate an ISBN. A ISBN registrar can help you do this.