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Chicago 18th edition (released September 2024) is the first major update to The Chicago Manual of Style in seven years. It replaced the 17th edition — which had been current since 2017 — with changes that affect book citations, author-count limits, footnote shortcuts, capitalization rules, and guidance on citing AI-generated content.
If you learned Chicago from a guide, class, or citation manager written for the 17th edition, almost everything you know about Chicago is now slightly wrong. The city in a book citation is gone. The number of authors you list before switching to “et al.” has dropped. The short form you use instead of “ibid.” has three shapes instead of one. And the rule for capitalizing the word after a colon has flipped.
These changes are not cosmetic. A student who formats their paper using Chicago 17 rules in 2026 will have inconsistent capitalization, too-long author lists in notes, and outdated publisher-city entries on almost every book reference. Most instructors won’t mark you down for the city — but they will notice the capitalization errors and the “ibid.” entries that break when you rearrange notes.
This article walks through every significant change, gives before-and-after examples you can copy, and tells you how to decide which edition to use when your professor hasn’t specified.
The Changes That Affect Every Student
These are the changes you will encounter on the first source you cite. They matter more than everything else in the 18th edition.
1. Book Citations: No More Place of Publication
What changed: The city and publisher location are no longer required in citations of books (CMOS §14.30).
Bibliography, 17th edition: Brown, Charles. The History of Everything. Oxford: Oxford University Press, 2021.
Bibliography, 18th edition: Brown, Charles. The History of Everything. Oxford University Press, 2021.
Footnote, 18th edition: Charles Brown, The History of Everything (Oxford University Press, 2021), 45.
This was one of the biggest simplifications in the edition. Every citation manager that still shows “City: Publisher” is using outdated output. If your paper cites forty books, that is forty lines of formatting you can delete.
Why this happened: The change aligns Chicago with modern publishing practice, where the city is no longer a reliable piece of metadata. Most publishers list their headquarters location regardless of where the book was actually produced or distributed.
2. Chapter Page Ranges Removed from Bibliography Entries
What changed: Chapter page ranges are no longer required in bibliography or reference-list entries, though they remain required in footnotes (CMOS §14.8).
Bibliography, 17th edition: Smith, Jane. “Revisiting the Renaissance.” In Oxford Handbook of History, edited by John Doe, 112–145. New York: Oxford University Press, 2020.
Bibliography, 18th edition: Smith, Jane. “Revisiting the Renaissance.” In Oxford Handbook of History, edited by John Doe. New York: Oxford University Press, 2020.
Footnote: Charles Brown, The History of Everything, 92–95.
The footnote still includes page numbers because the note points the reader to the exact location. The bibliography does not, because it already points to the whole chapter.
3. Author Limits Lowered — This Is the Sneakiest Change
The 18th edition reduced the number of authors you list before using “et al.” — and it reduced it differently for footnotes than for bibliographies. This is where most errors will hide, because a citation with the wrong number of names still looks perfectly normal.
| Context | 17th edition | 18th edition |
|---|---|---|
| Bibliography / reference list — list all authors before “et al.” | Up to 10 | Up to 6 |
| Bibliography / reference list — if more than 6 | First 3 + “et al.” | First 3 + “et al.” (unchanged) |
| Footnote or author-date in-text citation — list all authors before “et al.” | Up to 3 | Up to 2 |
| Footnote or author-date in-text citation — if more than 2 | First 3 + “et al.” | First + “et al.” |
Bibliography entry, four authors, 18th edition: All four names are listed, because six is the new ceiling.
Footnote, four authors, 18th edition: Only the first name, followed by “et al.,” because a footnote now lists at most two.
If you learned Chicago from a guide or course written for the 17th edition, your instinct will be to list three names in a footnote and up to ten in a bibliography. Both of those are now wrong.
4. “Ibid.” Is Officially Replaced by Shortened Citations
The 17th edition already discouraged “ibid.” The 18th edition replaces it entirely by giving the shortened citation three clear forms (CMOS §13.37):
- Author and title (the regular short form)
- Author only
- Title only
17th edition (18th still accepts this, but discourages it): Charles Brown, The History of Everything, 92.
18th edition (preferred): Brown, History of Everything, 92.
The reason to prefer the shortened form over “ibid.” has nothing to do with fashion. “Ibid.” means the note directly above, so the moment you add a new source between two notes during editing, every “ibid.” below it becomes wrong. A shortened citation still points at the right book no matter how much you rearrange the notes.
5. Capitalization Rules Changed
The 18th edition updated two capitalization rules that affect running text and titles.
The word after a colon is now capitalized (CMOS §6.67). If the word after the colon begins a complete sentence, capitalize it. The new rule makes the capitalization mandatory, not optional.
17th edition: The study found: a significant increase in retention rates.
18th edition: The study found: A significant increase in retention rates.
Prepositions of five letters or more are now capitalized in title case (CMOS §8.160). This is a real change. Under Chicago 17, a preposition shorter than five letters was lowercase and anything five letters or longer was lowercase too. Chicago 18 flips that: “about,” “beyond,” “through,” and “between” are now capitalized in titles.
17th edition title case: The Psychology of Learning and How It Works
18th edition title case: The Psychology of Learning and How It Works
(That example looks the same because “how” is short. The difference appears with longer prepositions: “about,” “beyond,” “without,” “within,” “between.”)
6. A 3-Em Dash for Repeated Names Is Replaced by Repeating the Name
What changed: The 3-em dash (———) used to stand in for a repeated author name in consecutive bibliography entries is no longer preferred (CMOS §13.72). The manual now says to repeat the author’s name.
17th edition bibliography:
Brown, Charles. The History of Everything. Oxford University Press, 2021.
———. The Art of History. Oxford University Press, 2022.
18th edition bibliography:
Brown, Charles. The History of Everything. Oxford University Press, 2021.
Brown, Charles. The Art of History. Oxford University Press, 2022.
The 3-em dash was a space-saver. It is still technically permissible in the 18th edition, but the preferred approach is to just write the name again. Citation managers that output the 3-em dash need updating.
7. Presentation and Event Citations Simplified
Presentations cited in footnotes no longer use parentheses around the presentation details (CMOS §14.115).
17th edition: Charles Brown, “The Future of Digital Publishing,” presented at the 2020 Annual Meeting of the American Historical Association, San Francisco, CA, January 8, 2020.
18th edition: Charles Brown, “The Future of Digital Publishing,” Annual Meeting of the American Historical Association, San Francisco, CA, January 8, 2020.
8. New Guidance on Citing AI-Generated Content
The 18th edition adds explicit guidance for citing AI-generated text and images (CMOS §14.112). The 17th edition simply did not cover this because the tools did not exist in that form when the manual was published.
The practical approach is to credit the tool as the author, record the prompt and date, and treat the output as unrecoverable by the reader.
Example: ChatGPT. Prompt: “Explain the difference between qualitative and quantitative research methods.” Accessed October 15, 2025.
This is the kind of change that will dominate a student’s citation work in 2026 and beyond, because almost every student will have used an AI tool at some point during their research or writing process.
9. Journal Article Dates Simplified
A month or season can now usually be omitted in citations of journal articles (CMOS §13.26).
17th edition: Brown, Charles. “Teaching with Primary Sources.” Journal of History Education 15, no. 3 (Fall 2020): 45–67.
18th edition: Brown, Charles. “Teaching with Primary Sources.” Journal of History Education 15, no. 3: 45–67.
10. Other Notable Changes
The edition includes many smaller clarifications and additions that are unlikely to affect a student paper but are worth noting:
- Inclusive language: Expanded guidance on person-first and identity-first language, ableism, and gender-neutral options including singular “they” (CMOS §§5.51–267).
- Indigenous terms: “Indigenous” is now capitalized when referring to people; “Black” is usually capitalized; “White” may be capitalized if preferred by an author or publisher (CMOS §8.39).
- En dash for compound modifiers replacing hyphen: “Ali-Frazier match” becomes “Ali–Frazier match” (CMOS §6.85).
- Trailing slashes on URLs can usually be kept instead of dropped (CMOS §6.120).
- Month/day omission: A note that spans two pages can be cited as “10–11n5” rather than “10n5, 11n5” (CMOS §14.56).
- Alphabetization in indexes: The word-by-word system is now preferred over the letter-by-letter system (CMOS §15.66).
- Self-published books: “Published by the author” replaces “self-published” in citations (CMOS §14.36).
Chicago vs. Turabian: Which Should You Use?
Turabian is Chicago style adapted for students and thesis writers. Kate Turabian condensed the manual into a standalone guide for papers, theses, and dissertations. The citation rules inside Turabian have always tracked whichever Chicago edition was current.
Turabian 9th edition, published in 2018, follows Chicago 17. That is why a Turabian paper written today still carries publisher cities that the current Chicago manual dropped.
The University of Chicago Press has the 10th edition of A Manual for Writers scheduled for October 2026. The expectation is that it will bring the Chicago 18 citation rules across, including the missing publisher city and the new author limits, though the specifics are only confirmed when the book is actually published.
The practical rule for this term: If your course says Turabian, keep using Turabian 9th and the 17th edition patterns. Nobody is going to mark you down in October for following the handbook that was current when you started.
How to Decide Which Edition to Use
Both editions are in active use on campuses right now, and that is not going to settle until Turabian 10th ships. Here is how to decide without guessing:
| Your situation | What to use |
|---|---|
| The brief names an edition | Use that edition, even if it is the older one. The brief wins over any website. |
| The brief says “Chicago” with no number | Ask your instructor first. If nobody answers, use the 18th. |
| The brief says “Turabian” | Use Turabian 9th and 17th edition patterns. |
| You are submitting to a journal | Follow the journal’s “Instructions for Authors,” which often lag a year or two behind. |
| You already wrote half the paper in 17th edition format | Finish in 17th. One consistent edition beats a paper that switches halfway. |
Why this matters: Most citation guides, citation managers, and professor handouts still reflect the 17th edition. If you default to the 18th edition but your professor’s rubric expects 17th, you are not doing anything wrong — but you might lose formatting points. Always clarify with your instructor if they do not specify.
Your Citation Update Checklist
Use this list to audit your references for Chicago 18 compliance before submitting:
- Remove the city from book citations — check every book for “City: Publisher” and delete the city
- Check author limits — 6 in bibliography, 2 in notes; list first 3 + “et al.” if more than 6
- Replace “———” with author names in bibliography entries with repeated authors
- Replace “ibid.” with shortened citations (author + title)
- Capitalize the word after a colon in running text and titles
- Capitalize long prepositions (5+ letters) in titles
- Remove chapter page ranges from bibliography entries (keep them in footnotes)
- Remove months from journal article citations if not required by the journal
- Check AI citation guidance if you cited any AI-generated content
- Ask your instructor if the brief does not specify an edition
The Bottom Line
Chicago 18 is a real citation change, not a cosmetic one. The publisher city is gone from book citations, chapter page ranges are no longer in bibliographies, author limits have dropped, “ibid.” is replaced by shortened forms, and capitalization rules have been updated. There is also new guidance for citing AI-generated content and expanded inclusive language rules.
The changes affect almost every book you cite, and the author-count rules are the sneakiest part because a citation with too many names still looks fine at a glance. The safest move is to audit your bibliography against the checklist above and ask your professor if they have not specified which edition to follow.
What Should You Do Now?
If you are writing a paper that uses Chicago style, here is your action plan:
- Check your assignment brief for the edition your professor wants
- Audit your bibliography against the checklist (remove cities, check author counts, replace “———” and “ibid.”)
- Run your citations through a citation manager that supports Chicago 18 — most major ones have been updated
- Verify capitalization on titles and after colons
- If you cited AI content, add the new format from CMOS §14.112
Sources
Chicago 18th vs 17th Edition: What Actually Changed — practical breakdown with before/after citation examples