An International Standard Book Number (ISBN) is a unique identifier for a book or book-like item to allow that specific publication to be distinguished and located. An ISBN is applied to an individual item (e.g. one title or edition of a title) and is unique to that edition. For example, if a book is released as an eBook as well as a paperback, it should have two ISBNs, one for each format.
Serialised publications such as journals do not generally qualify for an ISBN and would usually have an ISSN. For more information about ISSN see ISSN International Centre - Requesting an ISSN.
Under the Copyright Act 1968, it is a legal requirement to deposit copies of a publication with the National Library of Australia. For all publications produced in Australia, legal deposit is also required at a number of NSW locations under the New South Wales Copyright Act 1879- 1952, ss 5-7.