How to Read an International Standard Book Number (ISBN)

If you’ve ever wondered how to read an ISBN and what all the numbers stand for then you’ve come to the right place. To most, an ISBN is just a random assortment of numbers much like a bar code, but to those in the book industry it’s a unique commercial book identifier. The ISBN was invented by Gordon Foster, an Emeritus Professor of Statistics at Trinity College in Dublin, in 1966. It was originally a 9-digit number, but it was increased to 10-digits in the 1970s, and 13-digits in 2007. So how does one go about reading an ISBN?  

The first point to note is that ISBNs are designed to be read from left to right. The second is that the important parts of an ISBN are separated by either a space or a hyphen (as in the example below). The third point to note is that an ISBN will have either 4 or 5 parts - 4 parts in the case of a 10-digit ISBN and 5 parts in the case of a 13-digit ISBN. The final point is that each part of the ISBN does not have a fixed number of digits, except for the check digit which is the last part of the number. The example we will use is the 13-digit ISBN seen below.

In a 13-digit ISBN the first set of numbers is referred to as a GS1 prefix. The GS1 system of product marking is an international standard developed for efficient supply chain management. Generally the GS1 prefix refers to a specific member organization, but in the case of books the GS1 prefixes of 978 and 979 have been allocated for use by all publishers. This is because the ISBN was in use long before the GS1 system was developed, so instead of replacing the ISBN system the GS1 system has found a way of blending it into their system by allocating these prefixes. The 3-digit GS1 prefix is also sometimes referred to as an European Article Number (EAN) or an International Article Number (IAN). In short, the first 3-digits of an ISBN don't mean much to the book collector.

The next part of the ISBN we will examine is referred to as the Group Identifier. In most cases, the Group Identifier is the 4th and 5th numbers of a 13-digit ISBN (or the 1st and 2nd numbers of a 10-digit ISBN). The Group Identifier refers to the language the book is published in. Most books have single digit Group Identifiers, but the Group Identifier can be anywhere between 1 and 5 digits long. Suffice to say, the rarer the language the book is printed in, the longer the Group Identifier. We have listed the single Group Identifiers below as they are the most common: 

0 or 1 for English speaking countries;

2 for  French speaking countries;

3 for German speaking countries;

4 for Japan;

5 for Russian speaking countries; and

7 for Peoples Republic of China. 

In the example above, the Group Identifier is only 1 digit long and given the digit is the number 1 we can tell the book is published in the English language. For a full list of Group Identifiers we suggest you visit the International ISBN Agency website and download the Range Message.

The third part of the ISBN is the Publisher Code. In the example above, the Publisher Code is 4 digits in length (4116), but publisher codes can stretch up to 9 digits. The Publisher Code is assigned by the ISBN agency. Publisher Codes are allocated in blocks and once a publisher has used all of their allocation they are assigned more blocks meaning that Publisher Codes are not always uniform or sequential. Unfortunately, there is no one place that you can look up all Publisher Codes, but a little creative searching online can lead you to some informal lists that are pretty accurate though not exhaustive.

The fourth part of the ISBN is the Item Number which in the example above is represented by the numbers 8691. The Item Number refers to the title of the book. Again, the title number can be varying digits in length and may only be a single digit.

The fifth and final part of an ISBN is the Check Digit which is always only 1-digit in length. The Check Digit is used as a form of error detection and is determined by a complex calculation using the other digits in the ISBN.

That's it!! I'll just finish off with a few words about the importance of ISBNs for book collectors. An ISBN is assigned to each edition, and each variation in format, of a book. This means that a first edition of a particular book will have a different ISBN to a second edition of the same book. This is why it's important to include ISBN information in any searches you are performing for a particular book, as sometimes just the title and author will not yield the exact book you are looking for. ISBNs also differ between formats (e.g. a hardcover version of a book will have a slightly different ISBN to a softcover version). In general, reprints of the same book (edition and format) will have the same ISBN.                                              

PS: It always bugs me that people write and read it as “ISBN number”. ISBN stands for International Standard Book Number. If you write “ISBN number” you are effectively writing International Standard Book Number Number. Call me crazy but you don’t need to write or read the word number twice. Get it right people!