You have seen ISBN barcodes on book covers, but what do the numbers in an ISBN mean? Although it may appear to just be a random sequence of numbers, each portion of the ISBN provides information about the book to which it is assigned.

An International Standard Book Number (ISBN) is a unique 13-digit number assigned to each title, edition and format of a book, ebook, audio book or similar product. The ISBN is used to identify a specific book product, in much the same way a Universal Product Code (UPC) identifies other products.

There are five parts to an ISBN:

• Prefix
• Group or country identifier
• Publisher identifier
• Title identifier
• Check digit

The prefix is a three digit number that identifies the product type or industry. For books, the prefix will be 978 or 979.

The group or country identifier indicates the country or language in which the book was published. English-speaking countries will be indicated with a 0 or 1, the identifier for French speaking countries is 2, the group identifier for German-speaking countries is 3, 4 for Japan, 5 for Russian speaking countries, and 7 for China. The group or country identifier may have as many as five digits.

The publisher identifier specifies the publisher of record for that title.

The title identifier is assigned by the publisher to a specific title, edition and format of the book. For example, the first edition of a hardcover book would receive an ISBN. If the book is also issued in paperback, audio book and ebook formats, each format would receive its own unique ISBN. When a second edition is published, each format of the second edition would receive a unique ISBN. New ISBNs are not required when a book is merely reprinted.

The last digit of the ISBN is a check digit. The check digit is a single-digit number from 0 to 10 (with X used to represent 10) that is computed from the other 12 digits in the ISBN. The purpose of the check digit is to catch errors in the entry of an ISBN.

Let’s take a look at a real-life example of how this works. The ISBN for my book, The Mystery Shopper’s Manual, is 978-1-888983-30-2.

• 978 tells us that this number identifies a book.
• 1 identifies the book as originating in an English-speaking country, in this case the United States.
• 888983 is the code assigned to my publishing company, Special Interests Publishing.
• 30 is the title identifier the publishing company assigned to this book: the trade paperback 6th edition of The Mystery Shopper’s Manual.
• 2 is the check digit calculated from the other digits in the ISBN, using a formula established by the ISBN agencies.

The product identifier is always three digits, and the group identifier and check digit are always one digit each. The length of the publisher and title identifiers may vary. Together, they will contain eight digits, but large publishers will have shorter publisher identifiers than small publishers. That is because the large publishers will have more title identifiers in their block of ISBNs. Here is how that works:

ISBNs are assigned to publishers in blocks of 10, 100 and 1000. The ISBN for my book comes from a block of 100 numbers. That means that two digits are assigned to the title identifier and six to the publisher identifier. If the block of ISBNs contains 10 numbers, there would be one digit to identify the title and seven for the publisher. If the block contains 1000 ISBNs, there would be three digits in the title identifier and five in the publisher identifier.

It is important to know that the ISBN tells the book industry who the publisher is. That is why you only want to get ISBNs from the official agency and not borrow or buy an ISBN from another publisher. If you use their ISBN, it will appear that they, not you, are the publisher.

Although all of this may seem confusing, ISBNs help to keep book distribution orderly by making sure that each edition of each book has a unique identifier.

Cathy Stucker is the founder of http://SellingBooks.com/ and the author of The Mystery Shopper’s Manual.