# What is an ISBN?

An ISBN, or International Standard Book Number, is a 13-digit identifier for one format of one book. The publisher applies for it through a national ISBN agency. It identifies the book but gives no copyright or legal protection, and each format, such as a paperback or an EPUB, gets its own.

Last reviewed 30 October 2026. Web page: https://chapbook.ink/glossary/isbn/

## What it means in practice

KDP offers a free ISBN for paperbacks and hardcovers. It can't be used anywhere else, and the book's imprint then reads "Independently published". If you want to name your own imprint or print elsewhere, apply for your own ISBN through your country's agency.

An ISBN doesn't protect the book. The international agency's words are that it "does not convey any form of legal or copyright protection".

## How Chapbook uses it

**Edit details** has an optional ISBN field, with the hint "Only if you bought one; stores issue their own." Chapbook writes it into the EPUB's metadata beside the book's own identifier, and nowhere else: the copyright page of the PDF and Word document does not print it, and the paperback's back cover leaves the [barcode](/manual/launch-and-export/#make-the-paperback-cover) to KDP.

Because each format has its own ISBN, don't reuse one you bought for the paperback in this field.

## Made with Chapbook: The Pricing Playbook

The Pricing Playbook: How founders set a price they can defend, by Jane Founder. Nonfiction book, 9,862 words, 43 pages. A sample generated from one brief and exported unedited; it is not a customer's book. Read every page: https://chapbook.ink/examples/nonfiction/

The brief:

> A repeatable method for pricing software: customer interviews, a value metric, tiering, and setting numbers you can defend. Promise: A repeatable method for setting a price you can defend to customers, investors and yourself, validated by ten customer interviews in a week. Reader: A founder who priced by guessing or by copying a competitor and now has to defend or change the number. Voice: Direct second person with occasional first person; worked examples with fictional companies; tables where they clarify; no invented statistics or named studies: reason from mechanics and examples.

The outline the planner proposed:

1. Introduction (620 words)
2. Why Guessing Fails (1,014 words)
3. What You Are Actually Selling (1,004 words)
4. Interview Ten Customers (1,088 words)
5. Choose the Value Metric (979 words)
6. Draft Three Tiers (1,076 words)
7. Set the Numbers (1,130 words)
8. Say the Price Out Loud (1,063 words)
9. Revisit Every Quarter (994 words)
10. Conclusion (384 words)
11. Appendix: The Interview Script (475 words)

## Questions

### Do I need an ISBN to publish on KDP?

For a paperback or hardcover, yes. For an eBook, no: KDP's help page, checked on 30 October 2026, says eBooks don't require one, and it assigns an ASIN instead.

### Can I use a free KDP ISBN at another printer?

No. KDP says its free ISBNs can only be used on KDP and cannot be used to publish outside it. The imprint on one reads “Independently published”.

### Does Chapbook need an ISBN?

No. The field is optional and none of Chapbook's files needs one. Fill it in only if you already have an ISBN for the EPUB.

## Sources

- [International ISBN Agency, “What is an ISBN?”](https://www.isbn-international.org/content/what-isbn/10)
- [Amazon KDP, “What is an ISBN and Imprint Name?”](https://kdp.amazon.com/en_US/help/topic/G7DMSKCM9DVS65TC)
- [Amazon KDP, “What is an ISBN and Imprint?”](https://kdp.amazon.com/en_US/help/topic/G201834170)