An ISBN (International Standard Book Number) is a unique code that identifies one specific edition of one specific book in one specific format, used by retailers, distributors, libraries, and bookstores to track and order it. You need a separate ISBN for each format (paperback, hardcover, ebook, audiobook) of the same book. Whether you need to buy your own, or can use a free one from a platform, depends on where you plan to sell.
This is part of the Complete Guide to Self-Publishing. Pricing and specifics below are for the United States as of 2026; other countries have their own ISBN agencies and pricing, some of which are free through a government or library system.
An ISBN doesn't protect your work; that's what copyright does, and copyright exists automatically the moment you create the work, separate from any ISBN. What an ISBN does is give retailers, wholesalers, and libraries a standardized way to identify and order your exact book: this edition, this format, this title. Without one, most retail and library systems can't properly catalog or order your book.
Amazon KDP offers a free ISBN for print books. The trade-off: when you use a platform's free ISBN, that platform (not you) is listed as the publisher of record in industry databases. This has a few real consequences:
If there's any real chance you'll want to distribute beyond Amazon eventually, buying your own ISBN before your first publication avoids having to redo the setup later.
In the U.S., Bowker (myidentifiers.com) is the sole official ISBN agency. As of 2026, typical pricing is:
| Package | Price | Per ISBN |
|---|---|---|
| Single ISBN | $125 | $125 |
| 10-pack | $295 | $29.50 |
| 100-pack | $575 | $5.75 |
Because most books need at least two ISBNs (one for print, one for ebook, sometimes a third for a different print format or a fourth for audio), the 10-pack is the better value for almost anyone publishing more than a single format of a single book. ISBNs don't expire, so buying more than you need right now isn't wasted money if you plan to publish again.
When you buy an ISBN through Bowker (or your country's official agency), you choose a publisher name, which can simply be your own name or a personal imprint you create. That name is then what appears in industry databases as the book's publisher, which is part of what makes owning your ISBN meaningful for building credibility as an independent publisher over multiple books.
Only buy from your country's official agency (Bowker in the U.S.), or from a platform explicitly offering a free or included ISBN as part of its service; third-party resellers charging a markup on Bowker ISBNs, or other unofficial sellers, are best avoided. Keep in mind that an ISBN is not a copyright, and buying one doesn't register or protect your copyright in any way. Once assigned to a book, an ISBN can't be reused for a different book, even if that book goes out of print. And you'll need a new ISBN if you make substantial changes that constitute a new edition, change publishers, change the title, or publish a translation.
Have Questions About ISBNs and Publishing Setup?
Entrada Publishing can help you think through ISBN and distribution decisions as part of getting your book ready to publish.
Yes. Each format (paperback, hardcover, ebook, audiobook) of the same book needs its own separate ISBN.
For authors selling only on Amazon and comfortable staying there permanently, yes. If there's any chance you'll want to distribute to other retailers or libraries later, a purchased ISBN avoids having to redo your setup.
In the U.S. as of 2026, a single ISBN from Bowker costs $125, and a 10-pack costs $295 ($29.50 each). Pricing and availability differ in other countries.
No. Copyright exists automatically when you create a work and is separate from an ISBN, which only identifies the book for retail and library cataloging purposes.