ISBNs have been used since 1970, when the use of these identifying numbers was approved as a standardized practice. In 2007, ISBNs switched from a 10- to a 13-digit number. The ISBN system is used by more than 160 countries to identify publishers all over the world.
The 13 numbers of an ISBN number are divided by a hyphen into five parts. The first part of an ISBN always starts with 978. (This will be the case until the issuing agency decides otherwise.) The second part indicates the country where your material is published. The third part of an ISBN identifies the publisher. The fourth set of numbers indicates the title of the published work. The final numbers are referred to as a check digit, which validates the authenticity of your ISBN.
An ISBN can be used to help track down a book or other published work that you want to purchase. Also, you may decide to self-publish a work. If you self-publish your work, it's best to obtain an ISBN number.
An ISBN number is issued by R.R. Bowker, the only agency in the United States where you can purchase an ISBN. ISBNs can be purchased in blocks of 10, 100 or 1,000. Larger publishers purchase blocks in the 1,000s. You can take up to five years to use your ISBN before it expires.
Never sell or lend one of your ISBN numbers. The ISBN number identifies you as the publisher of a work. If you sell or lend an ISBN number, this will cause you to be falsely identified as the publisher of another publisher's work.