ISBN (International Standard Book Number) structure:

The ISBN is an agency-assigned data element . ISBNs are assigned to monographic publications by designated agencies in each country participating in the program.

An ISBN consists of ten digits comprising four groups separated by hyphens. The tenth digit is a check digit used as a computer validity check; it consists of a number between 0 and 9 or an uppercase X (for the arabic numeral 10). Procedures for validation of the ISBN by calculating the check digit and hyphenating instructions are in Information and Documentation - International Standard Book Numbering (ISBN) (ISO 2108).

A description of the ISBN structure and guidelines for recording qualifying information are found in 1.8 Standard Number and Terms of Availability Area of Library of Congress Rule Interpretations .