ISBNs are only for books and are not available for calendars or periodical publications.
If you are publishing a recurring product (for example, a monthly literary journal), you need an ISSN (International Standard Serial Number). ISSNs are free! An ISSN is an eight-digit number that uniquely identifies your periodical. Unlike ISBNs, which contain country and publisher prefixes, the ISSN simply identifies the periodical (not the publisher from whom it is available).
An ISSN distinguishes a particular periodical from others with which it might be confused. The ISSN also helps library patrons, libraries, and others who handle large numbers of periodicals to find and identify titles in automated systems more quickly and easily. In the US, ISSNs are administered by the National Serials Data Program (NSDP) of the Library of Congress.
A separate ISSN is required for each medium; that is, if your periodical is available in both Download and Print formats, you will need a separate ISSN for each distribution format. After you get your ISSN, you should add it to your periodical. Unlike ISBNs, where Lulu adds the barcode to your back cover, ISSNs are your responsibility. Insert the ISSN in your source file before uploading and publishing.
