How to Cite an Encyclopedia (and Wikipedia)

Your professor says “don’t cite Wikipedia” on the first day of class, but three weeks later you need a citation for a foundational definition you found in an actual encyclopedia – and the rules for reference works turn out to be genuinely different from citing a journal article or book. There’s usually no individual author, the entry can be revised after you’ve read it, and “edition” information is often missing or ambiguous. Wikipedia adds its own wrinkle on top: a page that could look different tomorrow than it does right now.

This guide covers a traditional encyclopedia entry in all six major citation styles, then walks through the specific rules for citing Wikipedia when your assignment allows it.

Encyclopedia Entry (No Named Author)

Most encyclopedia entries – print or online – are staff-written or compiled from multiple contributors without a byline. Here’s the example we’ll use: an entry titled “Photosynthesis” from Encyclopaedia Britannica, last updated online on March 12, 2024.

APA 7th Edition

Photosynthesis. (2024, March 12). In Encyclopaedia Britannica. https://www.britannica.com/science/photosynthesis

• With no named author, the entry title moves into the author position, same as any unauthored source
• “In” signals that the entry sits inside the larger reference work, italicized as the container

MLA 9th Edition

“Photosynthesis.” Encyclopaedia Britannica, Encyclopaedia Britannica, Inc., 12 Mar. 2024, www.britannica.com/science/photosynthesis.

• The entry title is in quotation marks; the encyclopedia’s name is italicized as the container
• The publishing organization (Encyclopaedia Britannica, Inc.) appears as the publisher, distinct from the reference work’s title even though the names look similar

Chicago (Notes-Bibliography)

Footnote:

1. “Photosynthesis,” Encyclopaedia Britannica, last modified March 12, 2024, https://www.britannica.com/science/photosynthesis.

Bibliography:

“Photosynthesis.” Encyclopaedia Britannica. Last modified March 12, 2024. https://www.britannica.com/science/photosynthesis.

• Chicago favors “last modified” over a plain publication date for reference works that update continuously, since there often isn’t a fixed original publication date to cite instead

Harvard

Encyclopaedia Britannica (2024) Photosynthesis. Available at: https://www.britannica.com/science/photosynthesis (Accessed: 20 March 2024).

• The publisher fills the author position when no individual or entry-level author exists
• An access date is required, since the entry is an online source that can change

IEEE

[1] “Photosynthesis,” Encyclopaedia Britannica, Mar. 12, 2024. [Online]. Available: https://www.britannica.com/science/photosynthesis

• The entry title leads in quotation marks since there’s no author to list first
• “[Online]” flags the source as web-accessed before the “Available:” URL

Vancouver

1. Photosynthesis [Internet]. Encyclopaedia Britannica; 2024 [updated 2024 Mar 12; cited 2024 Mar 20]. Available from: https://www.britannica.com/science/photosynthesis

• “[updated ...]” records the entry’s last revision date, in addition to the standard “[cited ...]” access date
• No periods in any abbreviated element, matching Vancouver’s usual convention

When an Entry Has a Named Author

Specialized scholarly reference works – the Stanford Encyclopedia of Philosophy is the most commonly cited example – do credit individual contributors for each entry. When that’s the case, cite the contributor the way you would any other author, with the reference work as the container:

APA: Marchetti, H. (2023). Climate ethics. In Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/climate-ethics

MLA: Marchetti, Helena. “Climate Ethics.” Stanford Encyclopedia of Philosophy, 2023, plato.stanford.edu/entries/climate-ethics.

Always check the entry itself for a byline before defaulting to the no-author format above – scholarly reference works credit authors far more often than general encyclopedias do.

Citing Wikipedia

Wikipedia is a fundamentally different kind of source from a traditional encyclopedia: any registered or anonymous user can revise an article at any time, which means there’s no single fixed version the way there is for a print encyclopedia or even a dated online entry. Many instructors discourage citing Wikipedia directly as a scholarly source, though it’s often acceptable for background context or in courses that specifically study online knowledge production. Confirm with your assignment guidelines before relying on it as a primary citation.

Using a Permanent Link

Because a Wikipedia article can change between when you read it and when your grader checks your citation, use the “Cite this page” tool in Wikipedia’s sidebar to generate a permanent link to the exact revision you consulted, rather than the live, ever-changing URL:

APA: Climate change. (2025, June 4). In Wikipedia. https://en.wikipedia.org/w/index.php?title=Climate_change&oldid=1234567890

MLA: “Climate Change.” Wikipedia, Wikimedia Foundation, 4 June 2025, en.wikipedia.org/w/index.php?title=Climate_change&oldid=1234567890.

Chicago footnote: 1. “Climate Change,” Wikipedia, last modified June 4, 2025, https://en.wikipedia.org/w/index.php?title=Climate_change&oldid=1234567890.

The revision-specific URL (marked by “oldid=” in the address) locks your citation to the exact text you read, so a later edit to the article can’t undermine your reference the way it could with the live page’s plain URL.

Why Professors Discourage Wikipedia as a Primary Source

Wikipedia articles are collaboratively written and don’t go through the same peer-review process as academic publishing, so any individual claim’s reliability varies depending on how carefully that specific section has been maintained. The stronger academic habit is to treat Wikipedia as a starting point rather than a citable authority: read the article for orientation, then follow its own footnotes to the original sources it cites, and reference those primary sources directly in your paper instead.

Style Comparison

Common Mistakes

1. Citing Wikipedia’s live URL instead of a permanent revision link. The article your reader sees later may not match the version you actually cited.
2. Treating “no individual author” as “no source information at all.” The publisher (Encyclopaedia Britannica, Wikimedia Foundation) still fills the author or publisher role.
3. Skipping the citation because the fact “feels like common knowledge.” Reference-work definitions can genuinely be common knowledge, but not automatically – see our guide on when a claim needs a citation before assuming an encyclopedia fact is exempt.
4. Confusing “Encyclopaedia Britannica, Inc.” (the publisher) with the encyclopedia’s title. They’re related but distinct elements in MLA and Chicago citations.
5. Forgetting to check for a named contributor on scholarly reference works before defaulting to the no-author format.

Encyclopedia and Wikipedia entries are also two of the most common sources students forget to check against the broader list of frequent citation errors – see our common citation mistakes guide for the rest. And since most reference-work entries have no listed author by default, our guide on citing sources with no author or date covers the same fallback logic in more depth if you run into an edge case not covered here.

APA Style covers reference-work citations directly, including how APA treats entries with and without individual authors.

Try It with CiteTools

Reference-work citations have their own quirks – no author, rolling update dates, permalink requirements for Wikipedia – that manual formatting often gets wrong. Paste the entry’s URL into CiteTools.io and get a correctly formatted citation in APA, MLA, Chicago, Harvard, IEEE, or Vancouver, publisher and update date handled automatically.