h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

ISBNs now have 13 digits. The algorithm is different.
Convert your 10-digit to 13-digit numbers at http://www.isbn-international.org/converter/converter.html

Barcodes can encode the full Latin alphabet (not case sensitive) and the ten numbers (0-9). A ten-character barcode for ISBNs would therefore be quite feasible. However, barcodes on consumer goods are always 13 numerical digits. (Actually, there are 16 digits in the barcode, but three are check digits: there's a six at the beginning, a six in the middle, and a six at the end. These sixes are shown as slightly longer lines, and are not written below the barcode. This makes barcodes a prime candidate for recognition as 'the mark of the beast, without which no man may buy or sell'.)

To make books fit in with the standard consumer goods barcodes, three digits must be added. So 978 is added to the beginning of the ISBN (similarly ISSN barcodes are prefixed with 977). This is not all. The final digit of an ISBN is calculated by modulo 11, which may result in an answer of 10, represented by X. This won't do in a consumer barcode, so a different system of check digits must be implemented. I don't yet know what that is, but from your link above I've found the ISBN Users' Manual at http://www.isbn-international.org/en/download/2005%20ISBN%20Users%27%20Manual%20International%20Edition.pdf which may explain things.

This has all been the case for years. The only thing that's changed recently is that publishers no longer give the 10-digit ISBN as standard.

Previously, ISBN (10-digit) appeared on copyright page and above the barcode. The barcode itself was 13 digits, and these 13 digits were also written below the barcode.

Then, on the copyright page, alongside the ISBN there appeared the ISBN-13.

Then the ISBN was renamed the ISBN-10, and the ISBN-13 became the ISBN.

And now the ten-digit ISBN often doesn't appear anywhere on the book.

I don't know why these changes have been made, but 13-digit and 10-digit ISBNs have both been around for a long time, and compliment each other. See http://www.books-by-isbn.com/0-14-018745-6 which gives both ISBNs for this book. (The ten- or thirteen-digit versions can be entered into the URL, with or without hyphens. All redirect to the same page. Clever.)

TRiG.

I've been cataloguing books recently. Most have 10-digit ISBNs and that includes books published since 2007. I've only found 2 13-digit ISBNs so far.

In fact, the application I use for cataloguing doesn't accept 13 digit ISBNs, unless I omit any kind of separation. This isn't too much of a problem. I just omit the first 3 digits (978) and recalculate the check digit, which is easy.

I'll have to reword that post. I've only found a few books that *only* have 13-digit ISBNs. Where the ISBN is shown on the back of the book, there'll be a 13-digit ISBN under the bar code, but there's usually a 10-digit ISBN above the bar code. In a few cases there's been just the 13-digit ISBN, but I've catalogued over 500 books so far and less than 10 have had only 13-digit ISBNs. That means less than 2% of my books use the 13-digit ISBN exclusively.