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International Standard Book Numbers (ISBNs) are unique numbers which identify published books. Each edition of a book (for example, hardcover, paperback, and electronic) has its own ISBN, so a bookstore can order the book based on the ISBN and be assured of receiving the desired edition. ISBNs are integral to the operation of on-line book vendors and distributors of electronic editions of books.

The ISBN standard was adopted in 1970 by the International Organisation for Standardisation (ISO) as ISO 2108. Initially, ISBNs were 10 character codes, with the first digits indicating the so-called “registration group”, which generally identifies the language of the publication. In 2007, ISBNs were extended to a 13-digit code compatible with the European Article Number (EAN) system of product identification, with a Unique Country Code (UCC) of 978 denoting “Bookland”, with 979 reserved for expansion of that address space as necessary. With the change to 13-digit codes, the original ISBNs were redesignated ISBN-10, and the new ones ISBN-13. Any ISBN-10 can be converted to an ISBN-13 with a UCC of 978, and any ISBN-13 in UCC 978 can be converted to an ISBN-10. ISBNs with a UCC of 979 cannot, however, be converted back to ISBN-10. As of this writing (late 2018), almost all ISBN-13s have a UCC of 978: I can't recall ever encountering one in 979, and I read a lot of books.

The ISBN-10 and ISBN-13 systems are very different. Both incorporate a check digit to guard against errors in manual transcription or machine scanning, but they use different algorithms. In ISBN-10, the check digit can range from 0 to 10, with the last character of the code using the letter “X” to denote a check digit with value 10. ISBN-13 uses the EAN checksum algorithm, which yields check digits from 0 through 9, and hence are all numeric. Both ISBN-10 and ISBN-13 can include non-alphanumeric delimiters, which often separate the prefix (for ISBN-13), registration group element, registrant, publication, and checksum, for example “978-0-471-64877-2”. These delimiters are of no significance in interpreting the number: a specification of “978.0.471.64877.2” or “9780471648772” is completely equivalent. Traditionally, the larger publishers always delimited their registrant number to show how big they were (a two or three digit number is prestigious), but increasingly now, you see ISBN-13s with no delimiters: just thirteen digits. The structure of ISBNs permits parsing its fields purely from the number without delimiters.

As one who reads and reviews a lot of books, I find myself frequently working with ISBNs. My site is an associate, and to pay the rent, I often need to turn ISBN-13s I cite in reviews into ISBN-10s which can be used in Amazon links (Hello! It's been ten years, Amazon. Gonna fix that one of these days?). Further, I find it vexing when publishers fail to punctuate ISBNs into their functional parts, or do it incorrectly.

ISBNquest is a Web application which performs a variety of operations on ISBNs.

Request Form

To look up an International Standard Book Number (ISBN), enter it in the ISBN field of the request form (which appears in blue at the top of the page) and press the “Query” button. This is the only required field; all of the others are pre-filled with defaults. Details of the fields are as follows.

You can enter either an ISBN-13 or and ISBN-10, with or without separators between the parts. For example, all of the following are valid specifications of the same book: “978-0-451-22873-4”, “9780451228734”, “0.451.22873.1”, and “0451228731”. You can use any character as a separator which is not valid within an ISBN-13 or ISBN-10.
Part delimiter
If specified, this character will be used to separate the parts in the ISBN-13 and ISBN-10 values displayed in the Interpretation and Analysis sections. The default is “−” which is the most commonly used separator. You'll also see periods and spaces used as ISBN part separators. If the part delimiter is void (which is different from a space), whatever delimiter appears first in the ISBN field will be used. Don't confuse the delimiter with a DeLameter unless you wish to attract the attention of the Galactic Patrol.
Amazon associate tag
When you link to books on Amazon from your writings on the Web, you can receive commissions when readers purchase the books to which you've linked. To do this, you need to sign up for an “associates account” and include the tag they assign you in the links. This field allows you to specify your associates account to be included in the generated links. The default is Fourmilab's account; if you don't have an account, I'll be happy to collect the commission so as not to let it go to waste.
Amazon site
This is the domain name of the Amazon site to be included in the links generated to purchase the book. The default is the “” site in the United States. If you're in the United Kingdom, you'd use “”; if in Japan, “”, and so on. Be sure the ISBN you name is actually available from the Amazon site you specify (you can verify this by testing the link provided in the Amazon Book Information section).

ISBN Interpretation

ISBN-13 and ISBN-10 representations

The specified ISBN will be parsed into its parts, then shown in both ISBN-13 and ISBN-10 forms, with and without delimiters between the parts. This makes it easy to copy and paste whichever form is appropriate to your application. ISBN-13s which begin with a prefix of “979” cannot be represented as ISBN-10s; a message will inform you in this circumstance.

ISBN-13 Analysis

ISBN-13 analysis

This section parses the ISBN-13 into its component groups. The Registration group is identified by its English-language name from the ISBN range database. An ISBN-10 will have similar parts, but there will be no prefix and the checksum will differ because it is computed by a different algorithm.

ISBN-13 Bar Code

ISBN-13 barcode

This section provides a bar code, compatible with the EAN-13 bar code standard, for the book. This is what you'll see on the covers of books so that they can be scanned in retail stores. If you're producing your own books, you can use this to generate a bar code to include on the cover. The bar code is shown at a reduced resolution: for a full resolution image you can save and use for publication, click the image.

Amazon Book Information

Amazon information on book

ISBNquest will attempt to look up the ISBN on the U.S. Web site and report what it found. For books published outside the U.S. and available only in those markets, this look-up may fail and no output will be reported. Unfortunately, the look-up mechanism we use only works on the U.S. site. However, many books published outside the U.S. can be found on that site. If the search returns information about the book, the following are shown (some fields may be absent if not present in the Amazon database).

Title of the work. This may include information not shown on the cover or title page, such as a series of works in which it appears.
Name of the author(s).
Name of the publisher. The publishing industry has a baroque complexity with parent corporations, publishing houses, and “imprints”. This is whatever Amazon told us it is, and may not agree with what you find on the book's copyright page.
Publication date
This is usually the date on which this edition was published. If the ISBN is, for example, the paperback for which a hardcover was previously published, the date will be that on which the paperback was published.
Pages in the book.
Language of the text.
Binding of the physical book.
This is a minimalist link you can use to cite the book in your writing, which will credit your Amazon associates account for purchases made through the link.
Kindle link
If a Kindle edition of the book is found in the database corresponding to the print edition given by the ISBN, a link is provided to it. Due to the structure of the Amazon database and regional marketplace restrictions, it is not always possible to automatically find the Kindle edition. You can usually (but not always) find the Kindle edition, if one exists, by following the link to the print edition and then looking for other editions on that page.
Cover image
Following the book information table, an image of the book's cover will be shown. This is usually the cover for the ISBN you specified, but on some occasions it may be for other editions of the same work.