Do I need to include a URL for books and journal articles I read online?

If your source is a book, and it is available in print, you do not need to include a link in the reference.

Journal article references should always include a URL or DOI if present. The only exception is if you are consulting the print version of the journal. In this case, you can end the reference after the page number(s).

What is a DOI?

A DOI (Digital Object Identifier) is a kind of permalink. DOIs are persistent, and never change. They link to specific information sources even if the website URL or domain changes.

Traditional URL links (beginning http://www. or https://www.) are vulnerable to a phenomenon known as link rot. This is when webpage links break over time, meaning the information becomes inaccessible. This is why you provide an access date when listing a URL in a reference, but not for a DOI.

DOIs exist for most common academic sources available online. You only need them for some references, usually journal articles or books/book chapters only available online.

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