Help on ISBN
ISBN stands for International Standard Book Number, and is a way of uniquely numbering commercial books. It has been in use since 1970, so most books published in the past forty years will have an ISBN, but books before 1970 will have a different identification number, if any.
Since January 1, 2007, ISBNs have been 13 digits long. Before then, ISBNs were 10 digits. 13-digit ISBNs are entirely numeric (i.e. include only numerals from 0 to 9) but 10-digit ISBNs sometimes included a capital X as the final digit due to the checksum system used to validate the numbers. (See Wikipedia for more about ISBN checksums.)
The ISBN number for a book, if present, can usually be found near the book's bar code. An example of a 13-digit ISBN and bar code is seen below.
