If you're publishing a book, you need an International Standard Book Number (ISBN.)
As I mention in Release Your Writing, they are available through R.R. Bowker Company, and must be issued in the name of the publisher. So, if you publish through a print-on-demand firm, the ISBN is in the firm's name. If you want to own the number, you would have to purchase a minimum of ten ISBN's at a cost about $245 plus $30 registration fee plus $25 per barcode or a total investment of $525
Now, I've learned RJ Communications has become an authorized agent for R.R. Bowker and is selling single ISBN's at about $125. In fact, his site shows a December special for $99.
If you are issuing only one book and really want the ISBN in your name, look into it and review the application at this site, rjcom.com
If you are more likely to stay with print-on-demand, or are publishing multiple book formats, such as: hardcover, trade paperback, ebook, audio book, etc., you might be happy to purchase the ten-pack.