Each item in Amazon.com is given a unique ASIN number. For books that have an ISBN, the ASIN and the ISBN are the same. Books without an ISBN and other materials are also given an ASIN by Amazon.
On Amazon's web site, a product's web address, or URL always contains its ASIN, and given an ASIN you can construct the product's URL in the following manner (as of Sept 2002):
So for Strunk and White's Elements of Style, 4th Edition, paperback, which has an ISBN of 020530902X, the corresponding Amazon product URL is:
A shorter form of the URL for most products is:
So the URL for Elements of Style, 4th Edition would become: