October 9


What Is An ISBN? The Ultimate ISBN Guide

ISBN stands for International Standard Book Number and is used as a product identifier for publishers, booksellers, libraries, and online retailers, enabling efficient ordering, listing, sales tracking, and inventory management.

This article is split into two parts: ISBN basics, which covers the fundamentals of ISBNs and the theory, and then ISBN Practical which covers what authors need to know and do.

Part I: ISBN Basics

Before we go into the practical parts of ISBNs, you might want to learn the more basic aspects to get an understanding of the foundations. If that doesn’t interest you, you can always skip ahead to the ISBN Practical section to learn about what to actually do.

How Many Digits Are In an ISBN?

ISBNs used to be just 10 digits in length, up to the end of December 2006, but since January 1st, 2007, ISBNs are 13 digits long. 

What Do the ISBN Numbers Mean?

The numbers are calculated using a proprietary formula and include a check digit to validate the number.

ISBNs are split into 5 unique chunks that are separated by spaces or hyphens. Two chunks or sections are fixed in length, and the other three chunks are variable.

Let’s explore what each element means:

Prefix Element (3 digits, fixed)

The prefix element of an ISBN is the part of the number indicating that it is an ISBN. Both 978 and 979 prefixes are reserved for this purpose.

Registration Group Element (1-5 digits, variable)

This element identifies the specific country, geographical region, or language area participating in the ISBN system. The length can vary from 1 to 5 digits, depending on the number of publishers within that region.

Registrant Element (up to 7 digits, variable)

The registrant element identifies the particular publisher or imprint (an imprint refers to a specific trade name or brand under which a work is published). This part of the ISBN can be up to 7 digits long, allowing for a large number of unique identifiers for different publishers or publishing entities.

Publication Element (up to 6 digits, variable)

The publication element identifies the particular edition and format of a specific title. It can be up to 6 digits long, allowing for differentiation between various editions, formats (such as hardcover, paperback, or ebook), and special versions of a book.

Check Digit Element (1 digit, fixed)

The check digit is the final digit of the ISBN and is calculated using a Modulus 10 system with alternate weights of 1 and 3. Its purpose is to validate the accuracy of the rest of the ISBN. If any part of the ISBN is entered incorrectly, the check digit will not match, indicating an error.

Why are ISBNs Important?

Because ISBNs are identifiers, without them, it would be nearly impossible to quickly and efficiently identify a specific book title, especially books that have the exact same titles or books that have multiple versions or editions. Just like citizens in a country have passport numbers that can tell two different John Smiths apart, books also have unique codes.

Part II: ISBN Practical

In this practical section, you’ll learn how to actually use an ISBN and any questions that you might have around using them.

Do ISBNs Copyright My Book?

No. Unfortunately not. An ISBN is simply a unique identifier used to track and manage books in the marketplace. It helps identify the book, its edition, and the publisher, but it does not provide copyright protection. 

To copyright your book, you will need to register it with the appropriate copyright office in your country.

What Type of Publication Can I Use ISBNs For?

ISBNs are assigned to individual, one-time, complete, and standalone publications like books. They are not meant to be used for serial publications such as journals, newspapers, encyclopedias, yearbooks, or multi-volume sets. Serials have their own identification systems, such as ISSN (International Standard Serial Number) designed specifically for their periodic and recurring nature.

Can I Use ISBNs for Book Series?

If a book series consists of standalone volumes that can be read independently (meaning each book has its own complete storyline or content), each book in the series should have its own unique ISBN. This allows each book to be cataloged, sold, and tracked independently.

Do Different Book Formats Require Separate ISBNs?

Yes, each book format (i.e. paperback, hardback) requires a separate & unique ISBN. If you choose to assign an ISBN to your e-book, then you’ll need another ISBN as well.

Does an E-Book Need An ISBN?

The use of ISBNs for digital books (e-books) is not mandatory in all countries, and the requirement varies depending on the publisher, distributor, and the platform through which the e-book is being sold. On platforms like Amazon Kindle, Apple Books, Barnes & Noble Nook, and others, they have their own identification systems to manage digital books, however, they do offer the ability to assign an ISBN to an E-Book, should you wish to.

Does an Audiobook Need An ISBN?

It depends on the country or platform that determines whether you need an ISBN for audiobooks, just like with e-books. 

If you are planning to distribute your audiobook through major digital platforms such as Audible, Apple Books, or Google Play, these platforms typically use their own unique identifiers for tracking and managing audiobooks, so they don’t require an ISBN.

If you are producing physical CD copies of your audiobook, then some retailers and distributors prefer or require you to have an ISBN for cataloging and sales tracking purposes. The same goes with submitting your audiobook to libraries & educational institutions, as they tend to require ISBNs as well.

Even if not required, it’s always good to assign an ISBN, just in case if you plan on having the most options available in the future.

Why Assign an ISBN to an E-Book?

Although ISBNs in most cases are not required for e-books, many self-published authors still choose to assign ISBNs to their e-books for the following benefits:

Easier Cataloging & Discovery: Most libraries and educational institutions require ISBNs be assigned to digital books because they ensure the e-book is properly cataloged in their databases, which makes it easier for these organizations and the end readers to discover the book.

Greater International Distribution: Having an ISBN assigned to your e-book could facilitate distribution in certain regions, as some retailers or distributors in specific countries may require ISBNs on digital versions.

Increased Professionalism: Having an ISBN puts your e-book in the league of the global book market, and enhances the credibility & professional profile of your digital book, making it more attractive to educational institutions, libraries, or other organizations who may be interested in cataloging it.

Allows Differentiating Editions: If you have multiple versions or editions of your e-book (such as different file formats), assigning unique ISBNs can help differentiate these editions, making it easier to help end readers identify the exact version they may be looking for.

Do I Need an ISBN as a Self-Published Author?

If you plan on publishing in print, then yes, you will need an ISBN for every version of your book. For example, you would need one ISBN for your paperback book, and one ISBN for your hardback book. You can optionally assign another ISBN to your e-book if you so choose (read the above section about the benefits of doing so).

Do I Need to Buy an ISBN?

There are typically two ways in which you don’t have to buy an ISBN, but each has their own limitations.

The first way is if your country’s ISBN agency freely gives out ISBNs, to promote publishing within their borders, especially for local authors and publishers. Other country’s ISBN agencies have a fee associated with securing an ISBN. If you’re lucky enough to be a resident of or be eligible to publish within a country that offers free ISBNs, then that’s great news! Otherwise, you may need to consider the second option. Check with your country’s ISBN agency to see if there is a fee or not.

The second way to secure a free ISBN is to check if the self-publishing platform that you plan to go with offers a “free” ISBN. For example, Amazon KDP (see below the full list) offers a “free” ISBN that you can assign to your print book as you configure it for distribution. The reason it’s in double quotes is because there is a major caveat: You cannot use that free ISBN anywhere else outside of that platform! This makes it severely limiting, especially if you want to self-publish your book through multiple platforms, channels, and distributors, or eventually have a traditional publisher take it on. Therefore, in the second option, it’s always better to buy your own ISBNs for maximum flexibility and options.

What Platforms Offer a “Free” ISBN?

Below is a list of platforms that currently offer “free” ISBNs. Remember, that you don’t own the free ISBN, and that it’s limited for use on that platform. Therefore, if you plan on self-publishing on multiple platforms, you’re better off buying your own ISBNs that you fully control.

  • Amazon KDP
  • IngramSpark (US Customers Only)
  • Draft2Digital
  • Lulu

Where Do I Buy an ISBN?

To purchase your own ISBNs, you’ll need to first locate your country’s ISBN agency and then follow their process for securing your own ISBNs. See the full list of global ISBN agencies here.

For quick access, below is a list of the ISBN agencies in English speaking countries:

Can I Buy ISBNs In Bulk?

Many of the ISBN agencies that offer ISBNs for a fee allow you to purchase bulk numbers to save money, leading to a lower overall cost per ISBN. You’ll need to check with your agency to see if they offer ISBNs in bulk.

Let’s say you’re self-publishing your book in three versions – paperback, hardback, and e-book, and assuming you’re planning to assign an ISBN to your e-book, then you’ll need a total of three ISBNs. Instead of purchasing three individual ISBNs, it makes more sense to buy a pack of 10, which leaves 7 left over for potential books or versions (possibly an audiobook?) that you may want to release in the future. You might also be saving a bit of money in the process as well.

How Are ISBNs Issued & Assigned?

ISBNs are assigned by each country’s ISBN agency and then issued to publishers or self-publishers that will register them to their book titles or variations. 

When ISBNs are purchased or requested, the agency will ask for the publisher’s name, however, if you are self-publishing, then you can list your name as the publisher if you are not self-publishing through your own company. If you are using a “free” ISBN from a print-on-demand platform like Amazon KDP for example, the publisher will be listed as “independently published”. If you would rather have control over what this name is (also known as an imprint), then it’s best to get your own ISBNs directly from an ISBN agency.

What is an Imprint?

In the publishing industry, an imprint refers to a specific trade name or brand under which a book or a line of books is published. All you need to know as a self-published author, is that the imprint can be your author name, a brand name you choose to self-publish your books under, or if you self-publish your books under your own company, then it can be the company name.

ISBNs vs. Barcodes

An ISBN is not the same as a barcode. The ISBN is the actual number, and the barcode is the visual representation of that number that allows for barcode readers to read the ISBN. The book barcode can also optionally contain another number (IAN or EAN [International or European Article Number]) that identifies the price of a book and the currency it’s sold in.

If you are self-publishing through a print-on-demand platform, these tend to automatically generate barcodes for you, either on the cover design template or after the cover has been uploaded to their platform.

Can You Reuse An ISBN?

Unfortunately not. Once an ISBN has been assigned to a published title or version of a book, it cannot be reused. If you want to publish another book or different version then you will need to use a new, unused ISBN.

In Summary

ISBNs are an important part of the self-publishing process, and by understanding what they are, why & what they are used for, and how to best use them, you will ensure that your self-published books will have the most options when it comes to distribution.

If you would like some guidance on the overall steps to self-publishing your book, then make sure to get our free “Self-Publishing Process Checklist”, which also includes post-publishing steps to marketing your book and getting the maximum exposure possible.


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