20th January 2021
Referencing Tips: What Are URLs and DOIs?
If you cite an online source in your academic writing, you will usually need to include a URL or a DOI in the reference. What are URLs and DOIs, though? And which should you use in your references? In this post, we explain the basics.
What Is a URL?
The abbreviation “URL” is short for uniform resource locator. URLs let your computer find a site or resource online, which is why they’re also commonly known as “web addresses.” For example, the URL for this blog is:
Some URLs (e.g., permalinks and PURLs) are stable and permanent. This means they will always point to the same page or article. As such, a permalink or PURL should keep working for as long as the host site is online.
Other URLs are less permanent, though, so they may stop working if a website is reorganized and content is moved or deleted from the old location.
Because of this instability, some citation systems require a date of access alongside a URL in references. This lets the reader see when you last accessed the source, which is useful if you suspect the content may change or move.
Some citation systems also have specific rules for how to write URLs. In MLA referencing, for instance, you do not need to include the “http://” bit at the start. You should therefore check your style guide for advice on writing URLs.
What Is a DOI?
“DOI” is short for digital object identifier. As this suggests, DOIs let you link to a resource online (e.g., a published document such as an ebook or journal article). You will usually find the DOI for an article on the host site or at the top of the first page.
Created, assigned, and standardized by the International DOI Foundation (IDF), DOIs are persistent and stable. You can thus use any DOI and be confident it will remain accurate for as long as the internet (or at least the IDF) exists.
Most modern referencing systems, including APA, MLA, and Chicago style, favor DOIs over URLs. However, the correct way to write a DOI in a reference will depend on the system. For instance, you can write DOIs as either a link or as metadata:
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This makes it important to check your style guide for advice (if you have one).
Should I Include a URL or DOI in My Reference?
For any online source you add to a reference list or bibliography, you should include either a URL or a DOI. This ensures the reader can access the sources you’ve used if required. When writing a reference for an online source, then, we suggest:
- Including a DOI if one is available. This should be the case with most journal articles and ebooks produced by academic publishers.
- Using a URL for online sources that do not have a DOI. If a permalink or persistent URL is available, use this. If not, you may need to include a date of access as well (check your style guide for further advice).
Whether and how to include a URL or DOI in a reference ultimately depends on the system you’re using and the source you’re citing, though. Likewise, the details of how to present URLs and DOIs vary between different referencing styles. As such, make sure to check your style guide if you have one.
You can also check out our other blog posts for advice on specific source types.
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