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ISBN, ASIN and every other book number, explained

What ISBNs, ASINs, barcodes, ISSNs, ISNIs, DOIs, subject codes and store IDs are, who issues them, and which ones a self-published book needs in each format.

By Daniel Rahl Jackson · 7 min read · Updated 23 October 2026

A book can carry half a dozen different numbers, but most authors need only one or two. The one that matters most is the ISBN, and even that is optional for ebooks in the biggest stores.

NumberWhat it identifiesWho issues itDo self-published authors need it?
ISBNOne format of one edition of a bookThe national ISBN agency where the publisher is basedFor print, yes; for ebooks and audio, only with some stores
ASINA product on Amazon or AudibleAmazon, automaticallyYou get one automatically
EAN-13 barcodeThe ISBN-13, printed so it can be scannedMade from your ISBNOn print covers, yes; KDP adds one for free
ISSNMagazines, journals and other serialsNational ISSN centresRarely
ISNIA person or organisation, including each pen nameISNI registration agenciesNo, it's optional
DOIAn object, with a permanent linkDOI registration agenciesOnly for academic work
BISAC and Thema codesA book's subject, not the book itselfBISG (BISAC) and EDItEUR (Thema)You choose them yourself, free
Store IDsA book's listing in one storeEach store, automaticallyYou get them anyway
LCCNA US Library of Congress recordLibrary of CongressOptional, and only for US publishers

ISBN: the International Standard Book Number

An ISBN is a product number for one specific version of a book. Since 1 January 2007 every ISBN has 13 digits and starts with 978 or 979; the digits that follow identify the country or language area, the publisher and the title, and the last is a check digit. Older ISBNs had 10 digits. An ISBN-10 becomes an ISBN-13 by adding 978 in front and recalculating the last digit.

ISBNs come from the national ISBN agency of the country where the publisher is based, not where the book is printed or sold, coordinated worldwide by the International ISBN Agency. If you publish your own book, you are the publisher. Some agencies are free, others charge, and many sell single numbers. Find yours with the agency finder. An ISBN gives no copyright protection.

When you need a new ISBN

Each format needs its own ISBN: paperback, hardcover, ebook and audiobook are separate products, and so are different ebook file formats sold separately. The International ISBN Agency's rules also require a new ISBN for:

  • a substantially revised edition
  • a translation or any other language edition
  • the same text under a new title
  • the book under a different publisher

A price change or unchanged reprint keeps the same ISBN, and marketing reasons alone don't justify a new one. An ISBN is never reused, even after a book goes out of print.

Free ISBNs from KDP, Draft2Digital and IngramSpark

Several self-publishing services give you an ISBN for free. The catch is the same everywhere: the number only works inside that service.

ServiceWhich booksPublisher shownWhere you can use it
Amazon KDPPaperbacks and hardcovers; not low-content books such as journals"Independently published"Only on KDP
Draft2DigitalAny book published through D2D, assigned automaticallyThe publisher name you enter, or your author nameOnly through D2D's services
IngramSparkBooks from US-based publishers onlyIngramSpark's imprint, Indy PubOnly on IngramSpark; IngramSpark owns it and it can't be transferred

A free ISBN is fine if that edition will only ever be sold through one service. If you want your own imprint name, or the same paperback on both KDP and IngramSpark, buy your own ISBNs. KDP's Expanded Distribution won't accept an ISBN already submitted for distribution elsewhere, so if IngramSpark supplies bookshops with your paperback, leave Expanded Distribution off.

ASIN: Amazon's own number

An ASIN (Amazon Standard Identification Number) is the 10-character code Amazon gives every product in its store, and every book on Amazon gets one automatically. That's why Kindle ebooks don't need an ISBN: KDP makes it optional for ebooks. Audible audiobooks have their own ASIN starting with B0, and on ACX you find your book by entering the Kindle edition's ASIN. Outside Amazon an ASIN means nothing.

Barcodes: EAN-13

The barcode on a printed book is the ISBN-13 itself, printed as an EAN-13 (or GTIN-13) barcode. GS1, which runs the global barcode system, has allocated the prefixes 978 and 979 to the International ISBN Agency (older guides call this "Bookland EAN"), so a book needs no separate barcode number from GS1. KDP adds a barcode to your back cover for free if your file has none, as long as that area is clear, and Draft2Digital places it on print covers you upload.

ISSN, ISNI and DOI

  • ISSN (International Standard Serial Number) is an 8-digit number for magazines, journals and other publications that continue indefinitely, issued by national ISSN centres. Books get ISBNs instead, though a series with no planned end can also have an ISSN as a whole.
  • ISNI (International Standard Name Identifier) is a 16-character number for a public identity such as an author or organisation; each pen name can have its own. You get one through an ISNI registration agency, which may charge a fee.
  • DOI (Digital Object Identifier) is a persistent identifier with a link that keeps working over time, issued by DOI registration agencies. It is worth having mainly if your book will be cited in academic work.

You may also see the ISTC (International Standard Text Code), meant to identify a text across all its editions. ISO withdrew it in 2021, so ignore it.

Subject codes: BISAC and Thema

Subject codes describe what a book is about rather than identifying it. BISAC headings, maintained by the Book Industry Study Group (BISG), are nine-character codes such as FIC000000 for FICTION / General, and the full list is free to browse. Thema, managed by EDItEUR, is a free multilingual scheme built for the international book trade. Amazon uses its own categories instead; KDP lets you pick three per book.

Store IDs

Every store gives your book its own internal number, with or without an ISBN.

  • Apple Books uses a numeric ID that appears in book links (books.apple.com/book/id followed by digits); BookTrendSpy uses it to follow books across the Apple Books charts in 34 countries. Apple doesn't require an ISBN, but one can only be entered the first time you submit a book.
  • Google Play Books doesn't require an ISBN either, and gives books without one an internal ID starting with GGKEY.
  • Kobo gives books without an ISBN its own identifier, which not all of its partner sites accept, and an ISBN can't be changed once a book is loaded.

LCCN: for US publishers only

The US Library of Congress issues free control numbers before publication through its Preassigned Control Number (PCN) program. It is open only to US publishers, including self-publishing authors with a US place of publication and phone number, and you must send the Library a copy on publication. Its fuller Cataloging in Publication (CIP) record has stricter criteria. Both are optional.

Which numbers do I actually need?

  • Kindle ebook sold only on Amazon: none. Amazon assigns an ASIN.
  • Ebook sold wide: KDP, Apple Books, Google Play and Kobo don't require an ISBN, and Draft2Digital assigns a free one for its own channels. Buy your own if you want one number and your own imprint everywhere, or if a distributor insists; IngramSpark needs one for every format it distributes. Never reuse a print ISBN for the ebook.
  • Paperback or hardcover through KDP: an ISBN is required, one per format: KDP's free one (publisher "Independently published") or your own. The barcode is free.
  • Paperback through IngramSpark: an ISBN for each format. US publishers can take IngramSpark's free one, which only works there; everyone else buys from their national agency. If the same ISBN is also on KDP, keep Expanded Distribution off.
  • Audiobook: Audible gives it its own ASIN, and you claim the title on ACX with your Kindle ebook's ASIN. If you distribute it elsewhere with an ISBN, use a new one, not your ebook or print ISBN.

After that, what affects sales is your price, categories and keywords. See the publishing glossary, and the guides to ebook royalty rates, print costs and royalties and audiobook royalties.

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