The same book, cited both ways
Start with the change you will meet on the first source you cite. Here is one book as a bibliography entry under each edition.
That is the whole difference: the city is gone. Section 14.30 of the new manual states that a place of publication is no longer required in citations of books. It reads like a small thing until you remember that a history essay might cite forty books, and that every one of them now looks different from the example in a guide written before 2024.
Chicago 18 by the numbers
These are the changes that affect the citations themselves, with the section number from the manual so you can check any of them.
| Rule | 17th edition | 18th edition |
|---|---|---|
| Place of publication (14.30) | Required in book citations | No longer required |
| Chapter page range (14.8) | Required in the bibliography entry | No longer required |
| Authors in a bibliography (13.23) | Up to ten listed, then et al. | Up to six listed, then first three and et al. |
| Authors in a note (13.23) | Up to three listed, then et al. | Up to two listed, then first and et al. |
| Repeat citations (13.37) | Shortened form, with ibid still permitted | Three shortened forms: author and title, author only, or title only |
| URLs (6.120) | Trailing slash usually dropped | A trailing slash can usually be kept |
| AI sources (14.112) | No guidance, the tools did not exist | New guidance on citing AI generated content |
The author limits are the sneaky one
The publisher city is obvious once you know. The author counts are not, because a citation with the wrong number of names still looks perfectly normal on the page. Chicago 18 lowered both limits, and notes and bibliographies now behave differently from each other by a wider margin than before.
If you learned Chicago from a guide written for the 17th edition, your instinct will be to list three names in a note and up to ten in a bibliography. Both of those are now wrong, and both are invisible to a spell checker.
Ibid is quietly retiring
The 17th edition already discouraged ibid, and the 18th goes further by giving the shortened citation three clear shapes: author and title, author alone, or title alone. Chicago calls author and title the regular short form, and it is the one to reach for by default.
The reason to prefer this 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, every ibid below it becomes a lie. A short form still points at the right book no matter how much you rearrange.
Which edition should you actually use
Both editions are in active use on campuses right now, and that is not going to settle until the Turabian handbook catches up. 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 the instructor first. If nobody answers, use the 18th, since it is the current manual |
| The brief says Turabian | Use Turabian 9th, which follows Chicago 17, until your department adopts the 10th edition |
| You are submitting to a journal | Follow the journal instructions to authors, which often lag a year or two behind |
| You already wrote half the paper in the 17th | Finish in the 17th. One consistent edition beats a paper that switches halfway |
What happens to Turabian in October 2026
Turabian is Chicago in student form. Kate Turabian condensed the manual for papers, theses and dissertations, and the citation rules inside have always tracked whichever Chicago edition was current. The 9th edition, published in 2018, tracks Chicago 17, which 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 sensible expectation is that it brings 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 in hand. We will update this page once it ships.
The practical read 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.
Frequently asked questions
The bottom line
Chicago 18 is a real citation change, not a cosmetic one. Drop the publisher city, treat chapter page ranges as optional, list up to six authors in a bibliography and two in a note, replace ibid with a short form, and you have covered almost everything a student paper will touch. Then check which edition your course wants, because Turabian users are still on the 17th edition patterns until the 10th edition lands in October 2026.