ISBN stands for International Standard Book Number. An ISBN is a special code on a book, which indicates a book’s identity in an international registry. Today, an ISBN almost always corresponds to the number on a book’s barcode, but sometimes the number is unique (if, for example, the seller has changed the barcode for its own use). So, when looking for a book by code, you should always search using the ISBN.
The ISBN can be found at the back of the book above the bar code or on the copyright page, which is behind the title page. ISBNs come in 10 or 13 characters.
Matching an ISBN is especially helpful when distinguishing between books that might have a similar name, when making sure you have the right edition, or when sorting through books with the same authors and similar subjects. Most importantly, an ISBN is registered internationally, so that means you can use it to find a book anywhere!