Chicago is the standard citation style in history, theology, art history, and parts of philosophy — and it is the only major style that comes in two completely different forms. Which one you use depends on the field and the department, not on taste. This guide walks you through both variants under the current 18th edition, the main source types, and the places Chicago theses routinely drop marks.
A note upfront: all author names and DOIs in the examples below are illustrative — they show the form, don’t copy them as evidence.
Two systems, one manual
The Chicago Manual of Style (CMS, currently 18th edition, 2024) defines two parallel citation systems:
- Notes and Bibliography (NB) — footnotes in the text plus an alphabetical bibliography. Fields: history, theology, art history, literary studies, philosophy.
- Author-Date — author-year citations in parentheses plus a reference list. Fields: natural and social sciences, parts of economics.
You pick one and stick with it. Switching between footnotes and parenthetical citations halfway through a thesis is the most visible formal mistake Chicago has.
| Element | Notes-Bibliography | Author-Date |
|---|---|---|
| In the text | Superscript footnote number | (Mueller 2023, 42) |
| Citation location | Footnote at the bottom of the page | Parenthetical in running text |
| End list | Bibliography, alphabetical | Reference list, alphabetical |
| Main use | Humanities | Sciences |
Variant 1: Notes and Bibliography
The first-time footnote
The first time you cite a source, it gets a full footnote with all bibliographic details:
¹ Anna Mueller, City and the Social Question: A History (Suhrkamp, 2023), 42.
The comma before the page number is not optional, the book title is italic, publisher and year sit in round parentheses.
Place of publication: since the 18th edition, Chicago no longer requires a place of publication for books (CMS 18, 14.30); publisher and year are enough. Books published before 1900 are still usually cited with the place. Some departments still want the place for newer books too — then it goes before the publisher: (Frankfurt am Main: Suhrkamp, 2023). What matters is doing it the same way throughout.
For a journal article:
² Peter Schmidt, “Urbanization and Pauperism in the Vormärz,” Historische Zeitschrift 318, no. 2 (2024): 112.
Note the pattern: article title in quotes, journal title in italic, volume without “vol.”, issue number after “no.”, single page number after the colon.
The short form for repeat citations
The second and every later citation of the same source takes the short form: author surname, short title (one or two keywords), page number.
³ Mueller, City and the Social Question, 58.
What about Ibid.? The 17th edition already discouraged it in favour of the short form. The 18th edition (13.37) allows Ibid. only when the immediately preceding note cites exactly one source — and even then prefers the short form. The short form survives moving or deleting notes later. Some departments still ask for Ibid.; this is a handbook question, not a guess. More on the abbreviations in Ibid., op. cit. and loc. cit..
The bibliography at the end
The same book appears in the bibliography as:
Mueller, Anna. City and the Social Question: A History. Suhrkamp, 2023.
Differences from the footnote:
- Surname first (for sorting)
- Periods instead of commas between elements
- No parentheses around publisher and year
- No page number (that belongs in the footnote)
- Hanging indent from the second line
A journal article accordingly:
Schmidt, Peter. “Urbanization and Pauperism in the Vormärz.” Historische Zeitschrift 318, no. 2 (2024): 95–128.
The full page range of the article goes here — not the single cited page.
Variant 2: Author-Date
Author-Date is easier for anyone coming from APA. In the running text:
The social question of the nineteenth century was primarily an urban one (Mueller 2023, 42).
So: surname, year, page — no comma between name and year, but a comma before the page number. Subtly different from APA (Mueller, 2023, p. 42).
The reference list entry:
Mueller, Anna. 2023. City and the Social Question: A History. Suhrkamp.
The year moves directly behind the author’s name; otherwise the entry carries the same elements as the NB bibliography.
Multiple authors
The 18th edition reset the thresholds (CMS 18, 13.23 and 13.107):
- In notes and author-date citations, up to two authors are named. With three or more, only the first name appears, followed by
et al. - In the bibliography and reference list, up to six authors are listed. With more than six, the first three are listed, followed by
et al.
Examples:
- Footnote, two authors:
Schmidt and Weber, Industrial Revolution, 112. - Footnote, three or more:
Schmidt et al., Industrial Revolution, 112. - Author-date, two vs. three or more:
(Schmidt and Weber 2021, 112)vs.(Schmidt et al. 2021, 112) - Bibliography, four authors — all names, the first inverted:
Schmidt, Peter, Anna Weber, Lukas Hoffmann, and Maria Keller. - Bibliography, seven authors — the first three plus et al.:
Schmidt, Peter, Anna Weber, Lukas Hoffmann, et al.
The 17th edition used different numbers: et al. only from four authors in notes and author-date citations, and all names up to ten in the bibliography. Older handbooks and templates often still quote those figures. Check which edition your department follows.
Archival sources and unpublished material
Chicago is the historians’ standard because it handles archives cleanly. Footnote form:
⁴ Letter from Anna Mueller to Carl Reinmann, 12 March 1848, Mueller Papers, Collection N1234/42, German Federal Archive, Koblenz.
Elements in order: document type with sender and recipient, date, collection, shelf mark, archive, location. The shelf mark replaces the page number.
In the bibliography, archival material is often grouped by collection rather than by document:
Mueller Papers. German Federal Archive, Koblenz. Collection N1234.
How granular your department wants this is in the handbook — there is real variation here.
Online sources, online journals, databases
For online journals with a DOI, append the DOI as a link:
⁵ Bernhard Sicken, “Privates Kapital für öffentliche Aufgaben: Aktiengesellschaften in Preußen zum Ausbau der militärischen Infrastruktur zwischen Vormärz und Reichsgründung,” Historische Zeitschrift 302, no. 3 (2016): 650, https://doi.org/10.1515/hzhz-2016-0190.
For web pages without a publication or revision date, add an access date before the URL:
⁶ German Historical Museum, “Our Exhibitions,” accessed 15 October 2026, https://www.dhm.de/en/exhibitions/.
Chicago only asks for an access date when the source carries no date of its own. Many departments want one for every online source anyway; that is in the handbook too.
Direct quotations: block quotes and ellipses
Direct quotations of up to roughly 100 words run in the main text with quotation marks. Longer quotes become block quotes — indented, no quotation marks, single-spaced, usually smaller. The footnote (NB) or parenthetical (Author-Date) comes after the final period:
The central thesis is that the social question was an urban phenomenon. Not only in the metropolises but also in medium-sized industrial cities, the pattern was visible. (Mueller 2023, 42)
Omissions are marked with three dots … (no square brackets in Chicago), additions in [square brackets].
Mistakes that routinely cost Chicago theses marks
- Systems mixed. Footnotes and parenthetical citations in the same thesis — formal disaster, visible at a glance.
- Wrong italics. Book titles italic, article titles in quotes — not the other way round. Many students italicise article titles, which is wrong.
- Footnote marker placed wrongly. Superscript and after the punctuation, not before:
… urban spaces.¹ - No page number in the first citation. Every footnote with a concrete claim needs a page number, including paraphrases — a claim without a locator is not a claim.
- Et-al threshold confused. Under CMS 18, notes and author-date citations switch to the first name plus et al. from three authors; the bibliography lists up to six, and beyond that the first three plus et al. Copying the 17th-edition numbers (from four, up to ten) out of an old template makes the citations inconsistent.
What Chicago doesn’t solve: whether the source backs the sentence
A formally perfect Chicago footnote tells the reader where they could look. It does not tell them whether page 42 actually says what the sentence in your main text claims. In history, where arguments run across dozens of scattered footnotes, this is a typical source of error: a footnote points to a page where the attributed information doesn’t actually appear in that form — or appears only loosely, in the subjunctive, or with the opposite sign.
Neither plagiarism software nor a reference manager catches this. Both check form and text overlap, never content.
Without an upload or signup, a prefilled example shows how fabricated and mismatched entries stand out in the check. Check a sample citation → For the full content check, upload your thesis plus the cited PDFs to Acurio — every footnote is matched against the source, claim against passage, including the page you cite.
Checklist before submission
- You use either Notes-Bibliography or Author-Date, not both.
- For NB: first citation in full, repeats as a short form; Ibid. at most right after a note that cites exactly one source.
- Book titles italic, article titles in quotes.
- Et al. from three authors in notes and author-date citations; in the end list up to six names, beyond that the first three plus et al.
- Footnote marker is superscript and comes after the punctuation.
- Every footnote with a concrete claim has a page number.
- Archival sources carry collection, shelf mark, archive, and location.
- Online sources use a DOI where available; access date when the page has no date of its own or your department asks for one.
Clear those points and you are formally safe. Whether the footnote carries the argument you attach to it is the question no style manual answers — that one you check yourself, or you have it checked.