If you intend to sell your books personally, one at a time, the ISBN shouldn’t be necessary. But if you plan on selling your books on the internet, in retail settings, or even mail order, the ISBN will be your books identifier for anyone who wants to purchase a copy.

ISBN is administered by R.R. Bowker in the United States. They assign numbers and register your titles in an international database.

There are four parts to the 13 digit ISBN. First is the country that the ISBN was created in, then the publisher’s prefix (publishers can have more than one prefix). Next is the unique identification number assigned to a particular title. Finally, the last digit was created by a mathematical formula that verifies the validity of the number.

The minimum ISBN numbers to be purchased is 10, currently around $250 (2007). While some publishers have unused numbers they can sell to you, they will list your book as published by the company you bought the number from. There are further registration fees and various expediting options available that could push the price in excess of $450. There is a $50 charge for paper applications (vs. online application) as of 2007.

R.R. Bowker offers an online log book to keep track of your ISBN records at a fairly nominal annual cost.

In the past few years the ISBN has grown from 10 to 13 digits. It’s relatively easy to convert an old 10 digit number to 13: R.R. Bowker has an online conversion tool.

If you have a revised edition of a book to publish, it should have a new ISBN to differentiate it from earlier edition(s). Your book manufacturer may offer to update the number for a small charge, but I know of a case where the manufacturer updated not the most current edition but a previous edition they had manufactured, causing distributors and stores to return the books to the publisher in unopened cartons. Safest (and cheapest) would be to update the number yourself and supply it to the printer. Even better, have a reputable graphics company that specializes in barcodes (my favorite is Infinity graphics) prepare a PDF file or physical film negative to supply to your manufacturer.

The ISBN should appear on the copyright page of your book and also on the back cover. By printing a barcode of the ISBN on the back cover you’ll assist the distributors and retailers who carry your book.

Common book barcodes are presented in the EAN-13 format but there are other formats (UPC) that may be useful depending on the retail outlets that will carry your title.

For information about SAN and ISSN visit the R.R. Bowker site.