Both ISBN and ISSN refer to numbers assigned to identify publications. The difference is in the type of publication. Is it a book or is it a periodical? ISBN stands for International Standard Book Number. This is the 10 or 13 digit code you'll be familiar with on the back of books. ISSN stands for International Standard Serial Number. This is an 8 digit number assigned to a serial publication. Think of a periodical, newspaper, or magazine that has regular issues. There are volumes and issue numbers already assigned, so there's no need for a separate number for each individual issue. So instead of assigning a number for each individual issue, there is a number for the entire periodical, that is, the ISSN. The ISBN and ISSN are frequently used in cataloging.