Chicago style is unusual among major citation systems because it is really two systems in one. The Chicago Manual of Style (CMOS), now in its 17th edition (University of Chicago Press, 2017), defines both a Notes-Bibliography (NB) system — used primarily in the humanities, history, and the arts — and an Author-Date system — used in the sciences and social sciences. Choosing the wrong one is a common mistake, and the formatting rules differ significantly between them.
This guide covers both systems with practical examples, explains when to use each, and highlights the errors that trip up even experienced writers.
The Notes-Bibliography system uses footnotes (or endnotes) for in-text citations, paired with a bibliography at the end of the document. When you cite a source, you place a superscript number in the text, and the full citation appears at the bottom of the page (footnote) or at the end of the chapter or document (endnote).
First reference: The footnote contains the full citation.
Subsequent references: Use a shortened form — typically author's last name, shortened title, and page number.
The bibliography lists all sources cited, in alphabetical order by author, using a slightly different format from the footnotes (inverted author name, periods instead of commas).
Key distinction: Footnotes use commas between elements and enclose publication details in parentheses. Bibliography entries use periods between elements and do not use parentheses around publication details.
The Author-Date system works like APA: brief parenthetical citations in the text (author's last name and year) linked to a reference list at the end of the document.
(García 2021, 45)
The reference list is alphabetical, double-spaced, with hanging indents — structurally similar to APA and MLA reference lists.
| System | Used in | Key signal |
|---|---|---|
| Notes-Bibliography | History, literature, arts, theology, philosophy | Footnotes or endnotes with superscript numbers |
| Author-Date | Sciences, social sciences, some business writing | Parenthetical (Author Year) citations |
Your instructor, journal, or publisher will specify which system to use. If no guidance is given, default to Notes-Bibliography for humanities work and Author-Date for social science or science work.
Footnote (first reference):
1. Author First Last, Title of Book (Place of Publication: Publisher, Year), page.
Example:
1. Tony Judt, Postwar: A History of Europe Since 1945 (New York: Penguin, 2005), 312.
Shortened footnote:
2. Judt, Postwar, 318.
Bibliography entry:
Judt, Tony. Postwar: A History of Europe Since 1945. New York: Penguin, 2005.
Footnote:
1. Author First Last, "Title of Article," Journal Name Volume, no. Issue (Year): page.
Example:
1. Hayden White, "The Value of Narrativity in the Representation of Reality,"
Critical Inquiry 7, no. 1 (1980): 5–27.
Bibliography entry:
White, Hayden. "The Value of Narrativity in the Representation of Reality."
Critical Inquiry 7, no. 1 (1980): 5–27.
Footnote:
1. Author First Last, "Chapter Title," in Book Title, ed. Editor First Last
(Place: Publisher, Year), pages.
Example:
1. Gayatri Chakravorty Spivak, "Can the Subaltern Speak?," in Marxism and
the Interpretation of Culture, ed. Cary Nelson and Lawrence Grossberg
(Urbana: University of Illinois Press, 1988), 271–313.
Bibliography entry:
Spivak, Gayatri Chakravorty. "Can the Subaltern Speak?" In Marxism and
the Interpretation of Culture, edited by Cary Nelson and Lawrence Grossberg,
271–313. Urbana: University of Illinois Press, 1988.
Footnote:
1. Author First Last, "Page Title," Website Name, Month Day, Year,
https://www.example.com/page.
Example:
1. Sarah Zhang, "The Last Children of Down Syndrome," The Atlantic,
December 2020, https://www.theatlantic.com/magazine/archive/2020/12/
the-last-children-of-down-syndrome/616928/.
Bibliography entry:
Zhang, Sarah. "The Last Children of Down Syndrome." The Atlantic,
December 2020. https://www.theatlantic.com/magazine/archive/2020/12/
the-last-children-of-down-syndrome/616928/.
In-text citation:
(Judt 2005, 312)
Reference list entry:
Judt, Tony. 2005. Postwar: A History of Europe Since 1945. New York: Penguin.
In-text citation:
(White 1980, 12)
Reference list entry:
White, Hayden. 1980. "The Value of Narrativity in the Representation of
Reality." Critical Inquiry 7 (1): 5–27.
In-text citation:
(Zhang 2020)
Reference list entry:
Zhang, Sarah. 2020. "The Last Children of Down Syndrome." The Atlantic,
December 2020. https://www.theatlantic.com/magazine/archive/2020/12/
the-last-children-of-down-syndrome/616928/.
Using footnotes and author-date citations in the same paper is incorrect. Pick one system and apply it consistently throughout.
"Ibid." (Latin for "in the same place") refers to the source cited in the immediately preceding footnote. If you cite a different source between two references to the same work, you cannot use "ibid." — use the shortened form instead.
CMOS 17 note: The 17th edition discourages "ibid." in favour of shortened citations, because "ibid." creates errors when footnotes are reordered during editing. Many instructors and journals still accept it, but shortened forms are safer.
Footnotes provide the citation, but the bibliography provides the reader with a consolidated, alphabetical list of all sources. Both are required in the Notes-Bibliography system.
Footnotes use commas and parentheses; bibliography entries use periods and no parentheses around publication details. Applying footnote formatting to the bibliography (or vice versa) is a common error.
When citing a specific passage, the footnote should include the page number. Citing an entire book without a page reference is appropriate only when you are referring to the work as a whole.
CMOS 17 no longer requires the place of publication for books published after 1900 — though many instructors still expect it. Check your assignment guidelines.
The definitive source is the Chicago Manual of Style (17th ed.), published by the University of Chicago Press (2017). The online version at chicagomanualofstyle.org is continuously updated. Turabian's A Manual for Writers of Research Papers, Theses, and Dissertations (9th ed., Turabian, 2018) is a student-focused adaptation of Chicago style and is widely used in graduate programs. The Purdue OWL also maintains a reliable Chicago style guide at owl.purdue.edu.
Whether you are working in Notes-Bibliography or Author-Date, formatting Chicago citations by hand is tedious — especially when switching between footnote and bibliography formats for the same source. DEEPNOTIS handles both Chicago systems: import your sources once and export correctly formatted footnotes, endnotes, or author-date references as needed.
The citation labels feature lets you tag sources by chapter, argument, or theme — making it practical to manage the reference lists of long-form projects like dissertations and monographs.
Chicago style rewards precision. Having a tool that applies its rules consistently lets you focus on the argument rather than the punctuation.
University of Chicago Press. (2017). The Chicago manual of style (17th ed.). University of Chicago Press. https://www.chicagomanualofstyle.org
Turabian, K. L. (2018). A manual for writers of research papers, theses, and dissertations (9th ed.). University of Chicago Press.
Purdue Online Writing Lab. (n.d.). Chicago Manual of Style 17th edition. Purdue University. https://owl.purdue.edu/owl/research_and_citation/chicago_manual_17th_edition/cmos_formatting_and_style_guide/general_format.html