A book’s ISBN (International Standard Book Number) is a unique code that comes in either 10- or 13-digit format. This number can often be found on the back of the book, within the copyright page, and listed on most websites alongside the publisher’s information. If you cannot locate an ISBN, you can search the book’s title and author on WorldCat to find additional information including the ISBN. 

For DVDs and CDs, the unique code can be it’s UPC (Universal Product Code) or ASIN (Amazon Standard Identification Number). These can often be found on the back cover or on the insert inside of the case. This information is also listed on most online retailer websites.