ISBN questions come up early for most self-publishing authors, and the honest answer is "it depends on the format." Ebooks, paperbacks and hardcovers are not treated identically, and the free option KDP offers is not the same thing as owning your own ISBN.
This guide separates the format-specific rules from the wider question of when owning your own ISBN is actually worth the cost, so you can make an informed decision rather than defaulting to whatever KDP suggests during upload.
What an ISBN is
An ISBN, or International Standard Book Number, is a unique identifier assigned to a specific edition and format of a book, used by retailers, libraries and distributors to track and order it. It is not a copyright registration and does not itself protect your work; it simply identifies which exact version of a book is being referred to. See rights and royalties, explained for how ISBNs relate to broader questions of ownership and control.
Ebook
Kindle ebooks published through KDP generally do not require an ISBN, because Amazon assigns its own internal identifier (an ASIN) to track and sell the Kindle edition. If you also plan to distribute the ebook through other retailers, some of those platforms may ask for an ISBN of your own, so check the requirements of each retailer you intend to use.
Paperback
Paperbacks published through KDP typically do require an ISBN. KDP offers a free ISBN as part of the setup process, or you can supply your own if you have purchased one independently. Which option makes sense depends largely on whether you want to appear as the publisher of record and whether you plan to distribute the same edition beyond KDP.
Hardcover, where currently supported
Where KDP supports hardcover publishing, similar ISBN rules to paperback generally apply, though it is worth checking KDP’s current hardcover-specific documentation directly, since hardcover was added to KDP later than paperback and its rules have been refined over time.
Free KDP ISBN
A free KDP-provided ISBN is a genuinely convenient option, particularly for authors who intend to sell exclusively through Amazon and do not plan wider print distribution. The trade-off is that the ISBN is generally tied to KDP and typically lists an Amazon-related publisher name rather than your own imprint, and it usually cannot be transferred for use with a different printer or distributor later.
Own ISBN
Buying your own ISBN lets you list yourself, or your own imprint name, as the publisher of record, and gives you a number you control independently of any single platform. In the UK, ISBNs are obtained through Nielsen, the official UK ISBN agency, at nielsenisbnstore.com; check their site directly for current pricing and purchasing options, since these can change and vary depending on how many ISBNs you buy at once.
Imprint
An imprint is essentially a publishing name under which your book is presented to the world; owning your own ISBN generally lets that imprint name appear as the publisher, rather than a platform-assigned name. Whether having a distinct imprint matters to you is a personal branding decision as much as a technical one.
ISBN ownership
Whoever’s name is registered against an ISBN with the national ISBN agency is recorded as the publisher for that specific edition. If a third-party service purchases and registers ISBNs in its own name on your behalf, it is effectively listed as the publisher of your book, which is worth being clear-eyed about before agreeing to any such arrangement.
Different formats
Each distinct format of a book, such as paperback, hardcover and, where required, ebook, generally needs its own separate ISBN, because the ISBN identifies a specific edition and format rather than the book in the abstract. This is why a single title can end up with two or three different ISBNs across its formats.
Editions
A genuinely new edition, such as a substantially revised second edition, typically needs a new ISBN, separate from the original edition’s number, since the ISBN system exists to distinguish between different versions of a work, not just different formats.
KDP and IngramSpark
This is where ISBN choice matters most. A free KDP ISBN is generally tied to KDP and is not transferable for use on a different platform, so if you want the same print edition available through both KDP and IngramSpark under one identifier, you will typically need to supply your own ISBN rather than use the free option. See KDP vs IngramSpark for how the two platforms relate more broadly.
International publishing
ISBN agencies are organised nationally, so where you buy an ISBN can be tied to your country of residence or business. UK-based authors typically buy through Nielsen, while authors elsewhere will have a different national agency; check the requirements relevant to your own location rather than assuming a UK process applies everywhere.
When to buy your own ISBN
Buying your own ISBN tends to make the most sense if you want to appear as the publisher of record, plan to distribute the same print edition through more than one platform, are building a longer-term imprint or catalogue, or simply want independence from any single platform’s free option. If you are testing the water with a single Kindle-exclusive ebook and no near-term plans for print or wider distribution, the free KDP option for any paperback edition may be perfectly reasonable to start with.
Common mistakes
- Assuming ebooks need an ISBN like print books. Kindle ebooks generally use Amazon’s own identifier rather than an ISBN; check current KDP rules rather than assuming print and ebook rules match.
- Using a free KDP ISBN, then wanting to move to IngramSpark. Free platform-provided ISBNs are typically not transferable, which can mean effectively creating a new edition to distribute elsewhere.
- Letting a service provider register ISBNs in its own name without realising it. This can make the provider the publisher of record for your book; check whose name appears with any ISBN purchased on your behalf.
- Reusing one ISBN across different formats. Each distinct format generally needs its own ISBN, since it identifies a specific edition and format, not the work as a whole.
- Not checking national ISBN agency rules. ISBN purchasing is organised nationally; UK authors should check Nielsen’s current guidance rather than assuming rules from elsewhere apply.
Frequently asked questions
Is a free KDP ISBN bad?
Not necessarily; it is a reasonable option for paperbacks sold exclusively through KDP, but it is generally tied to that platform and lists a platform-related publisher name rather than your own.
Where do UK authors buy an ISBN?
The official UK ISBN agency is Nielsen, at nielsenisbnstore.com; check their site for current options, since pricing and bundle sizes can change.
Do I need a different ISBN for each book format?
Generally yes; paperback, hardcover and, where required, ebook editions each typically need their own separate ISBN.
Can I use the same ISBN on KDP and IngramSpark?
You can generally use your own purchased ISBN across both, but a free KDP-provided ISBN is typically not usable outside KDP, so check current rules on both platforms before deciding.