Et Al. Citation Rules: APA, MLA, Chicago

“Et al.” (Latin et alii/et aliae, “and others”) is a scholarly abbreviation used to shorten a citation when a source has more than a style-specific number of authors. The rule that decides when to switch to “et al.” — and how many authors to name before doing so — is not the same across citation styles, and getting it wrong is one of the most common manuscript-formatting errors editorial offices flag before peer review even starts. This guide covers the current, verified author-count thresholds for APA, MLA, Chicago, and Vancouver/AMA (the biomedical style used by most ICMJE-following journals), plus punctuation, italicization, and the mistakes that recur most often.

The short answer: threshold by style

Every major style uses “et al.” to replace author names once a source exceeds a set author count, but the number of authors named before the abbreviation kicks in — and whether that rule applies from the very first citation of a source — differs by style. This table summarizes the current rules; the sections below cite the primary source for each.

Style	In-text citation	Reference list / bibliography
APA (7th ed.)	3+ authors: first author + “et al.” from the first citation onward	Up to 20 authors listed in full; 21+ authors: first 19, an ellipsis, then the final author (no “et al.” in the reference list itself)
MLA (9th ed.)	3+ authors: first author + “et al.” (parenthetical citations only — see the running-prose exception below)	3+ authors: first author + “et al.”
Chicago (17th ed.), author-date	3+ authors: first author + “et al.” (always, regardless of total count)	3–6 authors listed in full; 7+ authors: first 3, then “et al.”
Chicago (17th ed.), notes-bibliography	4+ authors in a note: first author + “et al.”; up to 3 authors named in full in notes	Up to 10 authors listed in full; 11+ authors: first 7, then “et al.”
Vancouver / NLM (ICMJE-endorsed)	Style uses numbered citations, not author names, in text	Up to 6 authors listed in full; 7+ authors: first 6, then “et al.”
AMA (11th ed.)	Style uses numbered citations, not author names, in text	Up to 6 authors listed in full; 7+ authors: first 3, then “et al.”

APA style (7th edition)

APA’s own style guidance is explicit and easy to misapply if a researcher is working from an older habit formed under the 6th edition. Under APA 7, a source with three or more authors is abbreviated to the first author’s surname plus “et al.” starting with the very first citation — not just on second and later mentions, which was the 6th-edition rule (under APA 6, three-to-five-author sources were spelled out in full on first citation, then shortened to “et al.” afterward; APA 7 removed that distinction). APA states the rule as: “For a work with three or more authors, include the name of only the first author plus ‘et al.’ in every citation (even the first citation).”

Examples: parenthetical — (Taylor et al., 2018); narrative — Taylor et al. (2018) found that.... Two-author sources are never shortened: both names are given every time, joined by “and” in narrative text or an ampersand in parenthetical citations (e.g., Chen and Diaz (2021) vs. (Chen & Diaz, 2021)).

Ambiguity exception: if shortening two or more different sources to the same “first author et al.” form would make them indistinguishable, APA instructs authors to write out as many author names as needed to tell the citations apart before switching to “et al.” for the remaining names.

The reference-list entry itself is unaffected by the in-text “et al.” rule: APA lists up to 20 authors by name in the reference list; only when a work has 21 or more authors does the reference list itself abbreviate, using an ellipsis between the 19th and final author rather than “et al.”

MLA style (9th edition)

MLA’s threshold is the same author count as APA — three or more authors triggers “et al.” — but MLA draws a distinction APA does not: where the citation appears. In a Works Cited entry or a parenthetical in-text citation, MLA uses “et al.” for three-plus-author sources: Cockcroft, Eva S., et al. in the Works Cited list, (Cockcroft et al. 42) parenthetically. But when a source is named in running prose rather than in a parenthetical, MLA’s own style guidance reserves “et al.” for the Works Cited list and parenthetical citations specifically, and instructs authors instead to spell out the authors’ names in full, or to name only the first author followed by “and others” (not “et al.”) in the sentence itself. This is a genuinely common formatting slip — dropping “et al.” into a sentence like “Cockcroft et al. argue that…” reads as fine by APA and Chicago convention, but is not the construction MLA’s own guidance describes for prose mentions.

Chicago style (17th edition) — two systems, two different rules

Chicago is the style most likely to trip up a co-author unfamiliar with it, because the Chicago Manual of Style maintains two citation systems with different “et al.” rules, and a manuscript typically uses only one, chosen by the journal or press.

Author-date system (parenthetical citations plus a reference list, common in the sciences and social sciences): in text, a source with three or more authors is always shortened to the first author’s name plus “et al.” — this does not change once a work has been cited before, unlike the reference-list rule. In the reference list itself, Chicago lists up to six authors by name; for seven or more authors, only the first three are named, followed by “et al.”

Notes-bibliography system (footnotes or endnotes plus a bibliography, common in the humanities): in a note, up to three authors are named in full; four or more authors are shortened to the first author plus “et al.” In the bibliography, up to ten authors are listed in full; eleven or more authors are shortened to the first seven, followed by “et al.” Note that this means the same source can be listed differently in a note versus the bibliography for the same manuscript — that is a real feature of the system, not an inconsistency to correct.

Vancouver / NLM style and AMA style (biomedical journals)

Biomedical and clinical journals that follow the ICMJE Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals generally point authors to the National Library of Medicine’s reference standards (Vancouver style, detailed in Citing Medicine, 2nd edition) rather than specifying an “et al.” rule of their own — the ICMJE Recommendations reference NLM’s standards rather than restating the author-count rule directly. Under NLM/Vancouver convention, a reference list entry names up to six authors in full; for seven or more authors, the first six are listed, followed by “et al.” Both Vancouver and AMA use numbered in-text citations (superscript or bracketed numerals) rather than author names, so the “et al.” question in these styles applies to the reference list, not to in-text mentions.

AMA style (used by JAMA, and widely across biomedical publishing) sets a different cutoff for how many names to spell out once the threshold is crossed: the AMA Manual of Style, 11th edition, lists up to six authors in full; for seven or more authors, only the first three are named before “et al.” — half as many as Vancouver/NLM’s first six. A manuscript prepared for a journal that follows AMA specifically (rather than NLM/Vancouver generically) should use the three-then-“et al.” form, not the six-then-“et al.” form, even though both styles are sometimes loosely grouped together as “biomedical citation style.” Check the target journal’s author instructions, since journals following ICMJE recommendations do not all specify identically formatted reference lists.

Punctuation and italicization

Period placement: “et al.” takes a period after “al” (short for the Latin alii/alia), but no period after “et,” since “et” is the complete Latin word for “and,” not an abbreviation. “Et. al.” and “et. al” are both incorrect.
No comma before “et al.”: the abbreviation attaches directly to the first author’s surname with no comma — Taylor et al., not Taylor, et al. — across APA, MLA, and Chicago.
Comma after “et al.” depends on the style and what follows: APA places a comma between “et al.” and the year in a parenthetical citation ((Taylor et al., 2018)); MLA’s parenthetical form has no comma before the page number ((Cockcroft et al. 42)). Follow the target style’s punctuation for the citation as a whole, not a fixed rule for “et al.” specifically.
Italicization: none of the major style guides — APA, MLA, or Chicago — currently italicize “et al.” in a citation, despite it being an unabbreviated Latin phrase. Like other common Latin abbreviations absorbed into everyday scholarly English (“etc.,” “i.e.,” “e.g.”), it is treated as standard English abbreviation, set in plain roman type. Italicizing it is a frequent overcorrection, especially from writers applying a general rule about italicizing foreign-language terms that does not apply to well-established Latin abbreviations in academic writing.

Common mistakes

Using the pre-2019 APA rule under APA 7. Spelling out three-to-five authors on first citation and shortening only afterward was the APA 6th-edition rule. Under APA 7, three-or-more-author sources are shortened to “et al.” on every citation, including the first.
Dropping “et al.” into MLA running prose. MLA’s own guidance reserves “et al.” for the Works Cited list and parenthetical citations; a source named in a full sentence should be spelled out or reduced to “first author and others,” not “first author et al.”
Confusing Chicago’s two systems. The author-date reference-list threshold (six authors) and the notes-bibliography threshold (ten authors in the bibliography, three in a note) are not interchangeable — using the wrong one is a common error when a co-author is more familiar with one Chicago system than the other.
Treating “Vancouver style” and “AMA style” as identical. Both are biomedical numbered-citation styles descended from the same tradition, but they set different author-count cutoffs before switching to “et al.” (six for Vancouver/NLM, three for AMA) — a manuscript formatted for one and submitted to a journal expecting the other will need its reference list corrected.
Adding a period after “et” or a comma before “et al.” Both are incorrect regardless of citation style.
Italicizing “et al.” out of habit. Not required, and not used, by any of the styles covered here.
Using “et al.” for a two-author source. Every style covered here requires both author names to be given for a two-author work; “et al.” only applies once a source clears the style’s specific author-count threshold (three for APA/MLA/Chicago author-date in-text, six or seven for the reference-list thresholds above).

Why the threshold differs by style at all

The differing thresholds reflect each style’s broader design priorities rather than an arbitrary inconsistency. APA and MLA are built around brief parenthetical or narrative in-text citations meant to stay unobtrusive in running prose, so both compress author lists aggressively (three authors is enough to trigger “et al.”). Chicago’s author-date reference list and Vancouver/NLM’s numbered-reference list are read more like a standalone bibliography than an in-line citation, so both tolerate longer author lists before compressing — reflecting biomedical and multi-author collaborative research norms, where six- and seven-author papers are routine rather than exceptional. Manuscript authors preparing a reference list should treat “how many authors before et al.” as a target-journal or target-style decision, not a fixed rule to memorize once and reuse everywhere — the correct threshold is the one specified by the venue’s actual submission guidelines or style manual edition, not a generic “citation rule.”

Frequently asked questions

How many authors before you use “et al.”?

It depends on the style and, for reference-list entries, on how many total authors the source has. For in-text citations, APA, MLA, and Chicago’s author-date system all shorten to “et al.” once a source has three or more authors. For reference-list/bibliography entries, the threshold is higher and style-specific: six authors under Vancouver/NLM and AMA before switching to “et al.,” six under Chicago author-date, and ten under Chicago notes-bibliography. There is no single universal number — always check the specific style and edition a manuscript is following.

Is there a period after “et” in “et al.”?

No. “Et” is the full Latin word for “and” and is never abbreviated, so it never takes a period. Only “al.” (short for alii/alia, “others”) takes a period.

Should “et al.” be italicized?

No, under any of the major styles covered here (APA, MLA, Chicago, Vancouver, AMA). It is treated as a standard scholarly abbreviation, the same way “etc.” and “i.e.” are, and is set in plain roman type.

Does APA still spell out authors on the first citation before switching to “et al.”?

Not since the 7th edition. Under APA 7, a source with three or more authors is shortened to the first author’s surname plus “et al.” from the very first time it is cited, not only on repeat citations. That was the APA 6th-edition rule, and applying it under APA 7 is a common formatting error in manuscripts revised from an older draft.

What’s the difference between Vancouver style and AMA style for “et al.”?

Both are numbered-citation biomedical styles, but they set different author-count cutoffs for the reference list. Vancouver/NLM style lists the first six authors before adding “et al.” when a source has seven or more authors. AMA style (11th edition) lists only the first three authors before adding “et al.” once a source has seven or more authors. A journal instructing authors to follow “AMA style” specifically expects the three-author form, not the six-author Vancouver form, even though the two styles are often discussed together as “the biomedical citation style.”

Can I use “et al.” for a source with only two authors?

No. Every style covered in this guide requires both authors to be named for a two-author source, both in text and in the reference list. “Et al.” only applies once a source’s author count crosses the style’s specific threshold.

Related CASRAI resources

For the broader landscape of citation-style differences beyond “et al.” specifically — including how each style handles DOIs, dataset citation, and reference-list ordering — see CASRAI’s Citation Styles and Referencing Formats overview. For the separate question of who qualifies as an author in the first place (as opposed to how author lists are formatted once determined), see the ICMJE Authorship Criteria guide and the Authorship dictionary entry. Researchers documenting each author’s specific role, rather than just formatting the author list, may also want CASRAI’s CRediT Author Statement Samples.