What is ISBN?

The International Standard Book Number (ISBN) is a numeric commercial book identifier.

The ISBN is a number that uniquely identifies content and is composed of five parts. The prefix element identifies the country, language area, and publisher of the book. The registrant element is the name of the publisher and can be up to seven digits long. The registrant element is only used in a single language and can be a combination of one and two digits. If the book is published by a single company, the ISBN is assigned to the company that published it.

The publication element of an ISBN is a 10 or 13-digit number that identifies the publication’s specific format and edition. The number can be up to six digits long. There is also a check digit that mathematically verifies the rest of the number. The digit ‘X’ is the check ‘X’ and is in upper case. The ISBN’s check ‘X’ is calculated using a modulus 11 system, but in some cases a Roman numeral is used instead of a ten.

The check digit is derived from the previous parts of the ISBN. The first number is multiplied by ten, each successive number by one less. The final number is multiplied by two. The products of these multiplications are added together, then the sum is subtracted from 11, and the result is the check digit number. This process is repeated for all five sections of the ISBN. The first section contains the country and region identifier, and the second section includes the language and publisher identifiers. The check digit is used for the validity of the entire number.

ISBN Barcode
A 13-digit ISBN represented by an EAN barcode

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