When you start tracking down books and articles for your research, you’ll notice a lot of strange-looking codes attached to them. These are identifiers—shortcuts that make it easier for libraries, publishers, and readers to keep track of exactly which work is being cited.
ISBN (International Standard Book Number): Every published book gets a unique ISBN, a 13-digit code (older books may have 10 digits). Think of it like a fingerprint for a book. If you want to be sure you’ve ordered the right edition—say, the 2015 vs. the 2021 printing—the ISBN will tell you.
ISSN (International Standard Serial Number): Journals, magazines, and newspapers don’t have ISBNs because they’re ongoing series rather than one-time publications. Instead, they use an ISSN, an eight-digit number that identifies the entire journal title (for example, Journal of American History).
DOI (Digital Object Identifier): Articles published online often include a DOI. This is a permanent link that will still work even if the website changes. Typing a DOI into https://doi.org/ will take you straight to the article’s official page.
Identifiers like these are broken up into components. Just looking at an identification code will tell you quite a bit about the item at hand:
Finally, you can convert these identifiers into URLs, so that typing them into a browser will take you to a record for the item. For ISBNs and ISSNs, remove any hyphens and then prepend the identifier with https://worldcat.org/isbn/ or https://worldcat.org/issn/, respectively. For DOIs, leave all punctuation intact and prepend with https://doi.org/: