# ISBN – What Does it Really Mean?

ISBN = International Standard Book Number

Most small and self-publishers know that an ISBN is a necessary number that identifies their book within the book industry. But what do all those numbers actually mean? Can anyone look at an ISBN and extract any useful information?

Let’s consider what the 13 digits in an ISBN mean to the book industry (publishers, wholesalers, distributors, libraries, and retailers).

First, note that you may encounter two versions of ISBNs — the ISBN-10 and the ISBN-13. Besides three more digits, what’s the difference?

A few years ago, the ISBN folks realized that they would soon exhaust the mathematical possibilities of the 10-digit format. Too many books were being published in too many different formats. The solution was obvious — expand the format to incorporate more digits. You might think that adding three more digits would increase the available numbers by a factor of 1,000…but you’d be wrong.

It only doubled them.

How could that be? you might wonder.

To answer that question, consider the bar code on the back cover of a book. You will usually find the ISBN printed in human-readable form (i.e., in numerals) just above the bar code. Up until a couple of years ago, that would have been the 10-digit ISBN. Then, during a transition period, it frequently included both the 10- and 13-digit forms of the ISBN. Now, most newly published books will show only the ISBN-13 (although some are still including both). You might also have noticed that there are human-readable numerals sort of embedded along the lower edge of the bar code. Those digits are the ISBN-13…and always have been (even when there was no such thing as an ISBN-13).

In the days of only ISBN-10, a book’s bar code with its embedded numerals (technically known as the Bookland EAN, or European Article Number) consisted of the ISBN-10 plus a 978 prefix and, usually, a different final digit.

Now, with the implementation of ISBN-13, the ISBN and the Bookland EAN will be identical, including the final digit.

Confused yet? Hold on. Let’s decode an ISBN-13 to help clear things up.

The ISBN-13 and Bookland EAN, consist of five distinct parts:

• 978 or 979 prefix (all this means is that the number refers to a book — after all, the EAN is used for a lot of other non-book products with their own unique prefixes)
• Group or country identifier (for books published in the English group — meaning the US, UK, Canada, Australia, New Zealand, etc. — this will a “0” or a “1”)
• Publisher prefix (this can from two to seven digits, depending on the size of the specific block of ISBNs)
• Title identifier (this is actually the part that is assigned to a specific title, edition, and format published by the publisher identified by the publisher prefix)
• Check digit (the last digit in the ISBN, always just a single digit, that is calculated using a specific mathematical algorithm and only really matters to computer databases and such — you don’t have to know how to compute it)

Note: To date, nobody has been assigned an ISBN block with the 979 prefix, although R. R. Bowker expects to begin issuing those later this year.

Since the ISBN-13 system allows for only two book-prefix possibilities (either 978 or 979), the change to ISBN-13 only doubles the available possibilities. One mystery solved.

Real-World Example: 978-1-934631-21-8

What does that string of numbers tell us?

Right away, you can see the “978” prefix that tells us this is a book. The next digit, the “1” following the first hyphen, says it was published in one of the English group countries. The next set of digits (934631) is the publisher prefix. If you looked up this prefix in one of the industry databases, like Books-in-Print, you would find out that “934631” identifies Slipdown Mountain Publications LLC…and only Slipdown Mountain Publications LLC. Nobody else will ever be issued that specific publisher prefix.

The next set of digits (21) represent one specific title, edition, and format in the block of “934631” publisher-prefix ISBNs. In this case, it is the first edition of my own book Devil in the North Woods and, specifically, the e-book format of that book. No other book will ever use the title identifier “21” with the publisher prefix of “934631” and the group identifier “0.” And that’s what makes it unique. And what makes sure nobody orders an e-book format for this book when they really wanted the paperback format.

Note: The paperback format of that same book has a different ISBN (in this case 978-0-9746553-1-4, which also has a different publisher prefix since our company owns two different blocks of ISBNs although both point only to us).

And then there’s the final, check, digit (8, in this case). The check digit calculation involves applying a mathematical algorithm to all the preceding digits (which is why the check digit for the ISBN-10 format is almost always different than the check digit for the ISBN-13 format of the same basic ISBN). The check digit can also be an “X,” which is used if the check digit calculation results in “10.”

By knowing the publisher prefix, you can immediately determine the size of that block of ISBNs. Since there are only 13 digits total, and the 978 (or 979 eventually) plus the group identifier always total four digits and the check digit is always a single digit, there are only eight digits left to work with. In the above example, the publisher prefix is six digits, leaving only two digits to assign to specific books and, thus, only 100 possibilities (00-99). Therefore, this represents a block of 100 ISBNs.

Since self-publishers usually buy a block of 10 ISBNs and small publishers typically buy a block 100, anyone who cares can quickly determine the size of your publishing venture. And they can determine that even if you leave out the hyphens…but that’s a lengthy subject better suited for a follow-up article.

If the ISBN for your book was assigned by one of the many subsidy publishers (who prefer to call themselves “self-publishing companies” or “POD publishers”), the publisher prefix will clearly designate that subsidy publisher as the publisher-of-record. Which means you did not really self-publish at all, as far as the book industry (trade journals, wholesalers, distributors, retailers, libraries, etc.) is concerned. Having a subsidy publisher listed as your book’s publisher is like starting your at-bat with two strikes already counted against you.

And that’s probably not the way you want to launch your book’s marketing campaign.