An ISBN (International Standard Book Number) is a controlled, 10- or 13-digit identification number allowing publishers, libraries, and book dealers to locate books. If you received an ISBN from Lulu, the ISBN will include Lulu's prefix and Lulu will be listed as the publisher of record. If you assigned an ISBN that you own to the project, your publisher info will be listed. For more information on the history and purpose of ISBNs, see http://www.isbn.org.
An ISBN is not needed to publish on Lulu (Lulu ISBNs are available for free in the Lulu Publishing Wizard). An ISBN is needed to have a book distributed outside of Lulu and entered into the book industry commerce chain.
If you are creating a new project for retail distribution, you will need a unique ISBN to identify it.
Please keep in mind that each version of your book — paperback, hardcover, eBook, or a newly released edition must be assigned a new ISBN to distinguish the title's edition and format (hardcover, paperback, eBook in EPUB format). This ensures your book is listed properly by bibliographic services, allowing both businesses and your fans to purchase the correct version of your book in their preferred format.
For information on how to obtain an ISBN, see the How to get an ISBN for a book.