The International Standard Book Number (ISBN) is a thirteen-digit number (it used to be ten-digits) that uniquely identifies books and book like products published internationally. The purpose of the ISBN is to establish and identify one title or edition of a title from one specific publisher and is unique to that edition, allowing for more efficient marketing of products by booksellers, libraries, universities, wholesalers, and distributors. If you have established your own publishing company—basically a name and an address to begin with—you can purchase ISBN numbers from R. R. Bowker, the U.S. agency licensed to sell them or from Self Publishing.com (an authorized agent of R. R. Bowker). If you are producing a softback and hardback version of your book, you will need two different ISBN numbers to identify them. The ISBN is printed on the copyright page of hardback and softback books, and on the lower portion of the back cover of softback books above the bar code.
Some major publishers place the ISBN on the back of hardback books, and some don’t, it really doesn’t matter. Let’s say you have started a publishing company and published your first book, assigning to it the first of your ten ISBNs you purchased. Be sure that when you have finished copies of your book, that you go back to R. R. Bowker, the database of record of the ISBN Agency and do what is required to be listed in Books in Print. This is a very important directory used by many bookstores. And always be sure to put your ISBN on all your promotional literature.