An International Standard Book Number (ISBN) is a unique code provided for all books and literature which identifies and classifies them by publisher, series, title and author. If you are producing any form of literature for sale, you need an ISBN to track sales of your book or book product.
For publishing companies that reside in the United States, the ISBN Agency is the only company that can provide ISBNs for publications. Any publishing agency that wishes to have an ISBN for their products, regardless of whether these are hard copy books, books on tape, or e-books, can request an ISBN.
To apply for an ISBN, the ISBN Agency for the country in which you're operating must be contacted directly, either via the agency's website and application form, or by telephone (to receive an application through the mail). In the United States, the website for applications and questions in www.isbn.org, but since there are over 160 ISBN agencies worldwide, if you are in a country outside of the US and are applying for an ISBN, your country's agency should be contacted directly. All applications to apply for an ISBN require a non-refundable application fee. The fee is specified on the application you receive for IBSN assignment.
ISBNs can also be issued right on the UPC barcode itself, to make for easy processing when selling a certain publication; this is easily requested by contacting the ISBN agency at the time of application. To correctly ensure that you're getting as many ISBNs as needed, they are only sold in solid number blocks. For this reason, it's better to overestimate the amount you may need, to avoid re-application fees if you find out later you'll need more ISBNS.
Once an application for an ISBN has been submitted, it can take anywhere from twenty-four hours to fifteen days to process and receive the ISBNs for your products. The ISBN is required for every format of the literature in question and for every revised version as well. After you receive the ISBNs for your literature, they need to be registered with the ISBN recording database for all ISBN agencies. ISBNs also cannot be reused after they are issued; this guarantees their originality as regards the specific publication. Every publisher is entitled to its own ISBN prefix, so try to buy blocks of ISBNs that will last a long time, guaranteeing your own publishing number will be reserved.