(This is abbreviated text from The Global Indie Author.)
What’s in a Number?
There are five parts to an ISBN, separated by either a hyphen or a space. Only the first three digits and the final check digit are of a fixed length; the remainder vary according to language, publisher identifier, and the number of ISBNs assigned to the block. The five parts of an ISBN are:
• the current ISBN-13 prefix of “978”;
• the group or country identifier;
• the publisher identifier;
• the title identifier; and
• the check digit which validates the ISBN.
For example, the ISBN for the Kindle version of Baby Jane is 978-0-9868914-0-3:
The ISBN prefix of “978” arose out of product barcode regulations that use the first three digits to identify the country of origin. When the ISBN and barcode systems were integrated for the purposes of publishing, books became a “country” in themselves, assigned the 978 prefix.
Publisher and Title Identifier
The next section, which is between one and five digits long, indicates the country identifier, with countries divided into language groups. The ones you will most commonly come across are single digits: “0” and “1” indicate English-language countries, “2” is for French, “3” is for German, “4” is for Japanese, and so on. Countries like Canada where we have two official languages, French and English, will see French-language books assigned “2” for the country code. Books published in an English-language country in a language other than English will still see “0” or “1” applied as the country code. For example, I noticed that Spanish-language books published in the U.S.—where Spanish is broadly adopted but not an official language—have “0” as their country code.
The publisher identifier and title identifiers are adjusted according to the number of ISBNs allotted in the block. If you are allotted a block of 10 numbers, the title identifier section will only be one digit (0 through 9); if you are allotted a block of 100 numbers, the title identifier section will be two digits (00 through 99); if you are allotted 1000 numbers your title identifier is three digits (000 through 999).
The publisher identifier is then lengthened or shortened to maintain the thirteen-digit format. Thus an English-language publisher allotted a block of 10 ISBNs will have a seven-digit publisher identifier while the same publisher allotted a block of 1000 ISBNs will have a five-digit publisher identifier number. Large publishers may be allotted even larger blocks, of 10,000 or even 100,000 numbers: