November 28, 2021
The ISBN (International Standard Book Number in English, "International Standard Book Number" or "International Standard Book Number" in Spanish)  is a unique identifier for books, [Note 1] intended for commercial use. It was created in the United Kingdom in 1966 by the British bookshops and stationers W. H. Smith and originally called Standard Book Numbering (in Spanish, ‘standard book numbering’), abbreviated SBN. It was adopted as an international standard ISO 2108 in 1970.
For periodical publications (magazines, newspapers), the International Standard Serial Number (ISSN, International Standard Serial Number) is used. 
This system allows:
Identify each book, as if it were its identity card, by registering the title, edition, publisher, print run, extension, subject, country, original language, etc .;
Systematize the editorial production of each country, by providing the elements that make statistics possible.
The ten digit ISBN
Until the reform that came into force in 2007, each edition and variation (except reprints) of a book received an ISBN composed of 10 digits in length, and divided into four parts:
the country code or language of origin,
the item number and
a check digit.These parts have different lengths and, to improve their readability (human readability), it is convenient, but not mandatory, that they be separated by blanks or hyphens. In addition, prefixes are used to ensure that two codes cannot begin in the same way.
If used, it must be placed correctly, the first dash was placed after the first digit, the second dash was variable in location, and the third dash after the ninth, just before the check digit. 
The country code was 0 or 1 for English-speaking countries, 2 for French-speaking countries, 3 for German-speaking countries, and so on. The original ISBN system lacked a country code, but prepending a 0 to a 9-digit SBN created a valid ISBN. The country code can be up to 5 digits long; for example, 99936 is used for Bhutan. You can consult the list of ISBNs by country.
The publisher number is assigned by the national ISBN agency, and the article number is chosen by the publisher.
Publishers receive larger blocks of ISBNs than they are expected to need; a small publisher may receive ISBNs consisting of one digit for the language, seven digits for the publisher, and a single digit for individual articles. Once you finish that block you can receive another one, with a different publisher number. So sometimes different publisher numbers actually correspond to the same one.
The check digit of a ten-digit ISBN is found by a calculation based on modulo 11: Each of the first nine digits is multiplied by the position they occupy in the numerical sequence, that is, the first by 1, the second by two and so on until the ninth that is multiplied by 9. Then these multiplications are added and the result is divided by 11. This division will leave a remainder between 0 and 10. If the remainder is between 0 and 9, this same value is that of the check digit. But if the remainder is 10, then the letter X is set as the check digit.
The thirteen digit ISBN
Due to the shortage of certain ISBN categories, the international standards organization adopted a thirteen-digit ISBN as of January 1, 2007. This update brings the ISBN system on par with the EAN barcode system.  Existing ISBNs are prefixed with "978" (and the check digit will be recalculated); when the ISBN "978" is exhausted, the prefix 979 will be entered