Few questions cause more early-stage confusion for self-publishing authors than whether an ISBN is compulsory. The honest answer is that it genuinely depends on what you are trying to do, and blanket statements in either direction ("you always need one" or "you never need one") are both wrong for some situation or other.
This guide walks through the main formats and distribution routes so you can work out what applies to your specific book, and points you towards the platform documentation worth checking before you commit to a setup.
Print books
For a physical, printed book intended to be sold through more than one platform, or through trade channels such as bookshops, wholesalers and libraries, an ISBN is generally required in practice. Trade ordering, cataloguing and library systems are built around ISBN lookups, and a print title without one is effectively unreachable through most of that standard infrastructure, even if a small run could technically be printed and handed out directly.
Amazon KDP offers a route around this for paperbacks and hardbacks sold exclusively through Amazon, by providing a free ISBN as part of the KDP publishing process. This lets an author publish a print book on KDP without purchasing an ISBN separately, though it comes with a trade-off covered below.
Kindle ebooks
At the time of writing, Amazon KDP does not require an author-supplied ISBN for a Kindle ebook. Amazon assigns its own internal identifier, the ASIN, automatically when the ebook is published, and this is generally sufficient for the book to be listed, sold and reviewed on Amazon’s Kindle store. Many authors who publish exclusively on Kindle never purchase an ISBN at all for that edition.
Other ebooks and wide ebook distribution
Requirements diverge more once you move beyond Kindle. Some ebook retailers and wide distribution services expect or require an ISBN to list a title, particularly where the distributor is aggregating a book out to multiple retail storefronts and needs a consistent identifier across all of them. Because this varies by platform and can change, check the current documentation for whichever ebook distributor or retailer you plan to use before assuming either that an ISBN is required or that it is not.
Hardcover
A hardcover edition is generally treated as a separate publication from a paperback of the same book, and so typically needs its own ISBN if it is being distributed as a distinct product, whether through KDP’s free option or a purchased ISBN for wider distribution.
Paperback
The same logic applies to paperback editions: if a paperback is being sold through KDP only, a free KDP-assigned ISBN is generally an option. If the same paperback, or a differently formatted paperback edition, is also going to be distributed through IngramSpark or another wider trade route, it typically needs its own separately obtained ISBN for that edition.
Audiobooks
Audiobook platforms have their own identifier conventions, and these are not consistent with print or ebook rules. Some audiobook distribution platforms use their own internal identifiers rather than requiring a publisher-supplied ISBN. Where an audiobook is intended for library distribution or wider trade cataloguing, an ISBN may be more relevant. Check the current requirements of the specific audiobook platform or distributor you intend to use.
Amazon-specific identifiers
It is worth being clear that Amazon’s ASIN and Amazon’s free KDP-assigned ISBN are two different things. The ASIN is Amazon’s own catalogue identifier, used for both print and ebook listings on its platform, and exists regardless of whether the title also has an ISBN. The free ISBN that KDP can assign to a print edition is a genuine ISBN, registered to an imprint associated with Amazon or KDP, and it exists specifically to satisfy the print trade’s ISBN requirement within KDP’s own system.
Retail distribution beyond a single platform
For example, an author who wants their paperback to be orderable through an independent bookshop’s usual wholesale supplier, rather than only through Amazon, will generally need the book distributed through a route such as IngramSpark, which in turn generally requires the title to carry its own ISBN, purchased by the author or publisher, rather than a platform-assigned one. This is one of the clearest practical cases where "do I need an ISBN" has a fairly firm answer: yes, if you want that kind of trade reach.
Libraries
Library systems and library suppliers typically rely on ISBNs to catalogue and order titles, including for independently published books. A book intended to be discoverable and orderable by libraries generally benefits from having a proper ISBN, ideally one registered to the author or their own imprint rather than a platform, since this affects how the book is recorded as a publication and how easily it can be catalogued.
Your own ISBN versus a platform-provided identifier
This is the decision that sits underneath most of the format-by-format detail above, and it is worth addressing directly. A platform-supplied identifier, whether Amazon’s free ISBN for print or an ASIN for Kindle ebooks, is genuinely useful and free, but it typically lists the platform or an associated imprint as the publisher of record, rather than you or your own imprint.
Buying your own ISBN, from your national ISBN agency, keeps you recorded as the publisher, and gives you more flexibility to move a title between distribution platforms in future without having to treat it as an entirely new edition. This does involve a cost, and current pricing should always be checked on your national agency’s official store, such as the Nielsen ISBN Store in the UK, rather than assumed.
The UK ISBN context
In the UK, ISBNs are issued through Nielsen, the official ISBN agency for the UK and Ireland at the time of writing, via the Nielsen ISBN Store. UK-based authors who want to be recorded as their own publisher should register and buy ISBNs directly through Nielsen rather than an unofficial reseller. See our fuller guide on where UK authors buy ISBNs for the practical steps.
When an ISBN is useful even if not technically required
Even where a platform does not strictly require an author-supplied ISBN, such as a Kindle-only ebook, some authors choose to buy one anyway. This is a genuine option worth considering if you expect to distribute the same book more widely later, want to be listed as your own publisher from the outset, or want consistent metadata across every edition and platform you might eventually use. It is not, however, a requirement, and there is no need to feel pressured into buying one for a format where the platform genuinely does not ask for it.
Common mistakes
- Assuming every format needs a separately purchased ISBN. Some formats, particularly Kindle-only ebooks, generally do not require an author-supplied ISBN at all.
- Assuming no format ever needs one. Wider print distribution, including IngramSpark, generally does require a proper ISBN, and skipping this can block distribution entirely.
- Not realising who is listed as publisher. Using a free platform-assigned ISBN typically lists the platform, not the author, as the publisher of record, which can matter later.
- Mixing up ASIN and ISBN. An Amazon ASIN is not a substitute for an ISBN outside Amazon’s own systems.
- Buying an ISBN from an unofficial reseller by default. Registering through the official national agency, such as Nielsen in the UK, keeps the process transparent and correctly recorded.
Frequently asked questions
Can I publish a paperback on Amazon without buying my own ISBN?
Generally yes, using the free ISBN KDP offers, though this typically lists an imprint associated with Amazon as the publisher of record rather than you.
Do I need an ISBN for a Kindle ebook?
At the time of writing, generally no; Amazon assigns its own ASIN for Kindle ebooks and does not require a separate author-supplied ISBN.
Do I need an ISBN to use IngramSpark?
Generally yes; IngramSpark distribution typically requires a title to have its own ISBN. Check IngramSpark’s current documentation to confirm.
Will not having my own ISBN stop me publishing at all?
No. Many authors publish successfully using platform-provided identifiers for Amazon-only publishing. The decision affects control and flexibility, not whether you can publish.
Does an audiobook need an ISBN?
It depends on the audiobook platform. Some use their own internal identifiers; others may expect an ISBN, particularly for wider or library distribution. Check current platform guidance.