An ISBN is an International Standard Book Number. ISBNs were 10 digits in length up to the end of December 2006, but since 1 January 2007 they now always consist of 13 digits. ISBNs are calculated using a specific mathematical formula and include a check digit to validate the number.
Each ISBN consists of 5 elements with each section being separated by spaces or hyphens. Three of the five elements may be of varying length:
- Prefix element – currently this can only be either 978 or 979. It is always 3 digits in length
- Registration group element – this identifies the particular country, geographical region, or language area participating in the ISBN system. This element may be between 1 and 5 digits in length
- Registrant element - this identifies the particular publisher or imprint. This may be up to 7 digits in length
- Publication element – this identifies the particular edition and format of a specific title. This may be up to 6 digits in length
- Check digit – this is always the final single digit that mathematically validates the rest of the number. It is calculated using a Modulus 10 system with alternate weights of 1 and 3.
