An International Standard Book Number (ISBN) is a 10 or 13 digit number that is a unique identifier for a book. If you have a copy of the publication, you can find the ISBN on the back cover (usually next to the barcode) or on the ‘copyright’ page. An International Standard Serial Number (ISSN) is a similar unique identifier for serials such as newspapers, magazines and journals. If you don’t have the publication with you, you can use catalogue services such as National Library of Australia’s Trove website to find the ISBN or ISSN.