After working in the library for almost 2 years, I have written down literally thousands upon thousands of ISBNs for books. After a while I noticed that books from the same country or from the same publisher had similar ISBNs. This made me curious, so I did a little research last year and found out how books are assigned their respective ISBN. It's kind of neat.
Here is how the number is broken out:
It's always 13 numbers long. The first three digits are always 978. I'm not sure why. Sometimes people leave off this prefix to have a 10 digit ISBN, but that practice is being phased out. The next section codes for the language the book is written in. The third section is the publisher, the fourth is the title (assigned by the publisher), and, finally, the last digit is the check digit.
The language number is kind of neat:
Here are the numbers that are assigned in the language section. The only things I've personally ordered with a language code of 4 are some comics for the Sampler section of the library. I guess there's not a lot of demand for other Japanese stuff...
Now let's look at the check digit.
If you don't want to do all the math, you can just use this website, which does it all for you. I use this quite often because people don't realize that the check digit changes when you add then "978" prefix to the ISBN.