An ISBN is a unique identifier assigned to every book. The ISBN is frequently printed above the bar code on the back of a book. ASIN stands for Amazon Standard Item Number. Every product in Amazon's catalog has a unique 10-digit ASIN which Associates use when they want to link to that specific item on Amazon.com. Historically, the ASIN assigned to a book was the same as its ISBN. For example, the ISBN for The Great Gatsby is 0743273567 and you can find it on Amazon at http://www.amazon.com/dp/0743273567. A recent Associates link to that book might look like this: http://www.amazon.com/dp/0743273567/?tag=assoc-id-20 while an older link might look like this: http://www.amazon.com/exec/obidos/ASIN/0743273567/assoc-id-20 .