Chicago style is the standard citation system in academic history, and is widely used in philosophy, literature, theology, and arts disciplines. It also has a social science variant. Unlike APA and MLA, Chicago offers two distinct citation systems — and using the wrong one for your discipline is a common error.
Two systems: which one do you need?
Notes-Bibliography (NB) — Used in history, literature, philosophy, theology, arts, and fine arts. Citations appear as numbered footnotes or endnotes; sources are also listed in a bibliography at the end.
Author-Date (AD) — Used in social sciences, natural sciences, and economics. In-text parenthetical citations (Smith 2021, 45); sources listed in a reference list at the end.
When in doubt, history always uses Notes-Bibliography. If your department says "Chicago style" without specifying which system, it is almost certainly Notes-Bibliography.
Notes-Bibliography System
How footnotes work
In the body of the essay, place a superscript number immediately after the cited passage, before any punctuation except a dash:
The testing effect has been described as "one of the most robust phenomena in cognitive psychology."¹
The evidence for spaced repetition is similarly strong,² though the optimal spacing interval remains debated.³
At the bottom of the page (footnote) or end of the document (endnote), each number gets a full citation on first use, and a shortened citation on subsequent references to the same source.
First footnote: full citation
Book:
1. Alan Baddeley, Michael Eysenck, and Michael Anderson, Memory,
3rd ed. (London: Psychology Press, 2020), 45.
Journal article:
2. Henry Roediger and Jeffrey Karpicke, "The Power of Testing Memory:
Basic Research and Implications for Educational Practice,"
Perspectives on Psychological Science 1, no. 3 (2006): 181–210.
Chapter in edited book:
3. Sarah Brown, "Working Memory in Academic Contexts," in Learning and
Cognition, ed. Jane Smith and Alan Jones (London: Routledge, 2021),
102–125.
Website:
4. Jane Smith, "How Spaced Repetition Works," BBC Future, March 15,
2023, https://www.bbc.com/future/article/20230315.
Subsequent footnotes: shortened citations
After a source has been given in full, subsequent references use a short form:
5. Baddeley, Eysenck, and Anderson, Memory, 87.
6. Roediger and Karpicke, "The Power of Testing Memory," 195.
Ibid. can be used when citing the same source as the immediately preceding note:
7. Baddeley, Eysenck, and Anderson, Memory, 120.
8. Ibid., 122.
Bibliography
The bibliography appears at the end of the essay on a new page. Unlike footnotes, bibliography entries:
- List the author's last name first
- Are sorted alphabetically by author's last name
- Use hanging indentation
- Do not include page numbers for the full work (books) but do for articles
Book:
Baddeley, Alan, Michael Eysenck, and Michael Anderson. Memory.
3rd ed. London: Psychology Press, 2020.
Journal article:
Roediger, Henry L., and Jeffrey D. Karpicke. "The Power of Testing
Memory: Basic Research and Implications for Educational Practice."
Perspectives on Psychological Science 1, no. 3 (2006): 181–210.
Note the difference between footnotes and bibliography:
- Footnotes: first name first, commas between elements
- Bibliography: last name first, elements separated by periods
Author-Date System
In-text citations
The Author-Date system uses parenthetical citations with the author's last name, year, and page number:
| Situation | Format | Example |
|---|---|---|
| Standard | (Author Year, page) | (Smith 2021, 45) |
| Author in sentence | Author (Year, page) | Smith (2021, 45) argues... |
| Two authors | (Author and Author Year, page) | (Smith and Jones 2021, 45) |
| Three or more | (Author et al. Year, page) | (Smith et al. 2021, 45) |
| No page (e.g., website) | (Author Year) | (Smith 2021) |
Note: Chicago Author-Date does not use a comma after the author's name (unlike APA). The format is (Smith 2021, 45) not (Smith, 2021, p. 45).
Reference list
The reference list is alphabetical and uses the same information as the bibliography but formatted slightly differently:
Book:
Baddeley, Alan, Michael Eysenck, and Michael Anderson. 2020. Memory.
3rd ed. London: Psychology Press.
Journal article:
Roediger, Henry L., and Jeffrey D. Karpicke. 2006. "The Power of
Testing Memory: Basic Research and Implications for Educational
Practice." Perspectives on Psychological Science 1 (3): 181–210.
The key structural difference from Notes-Bibliography: the year moves to after the author's name in the reference list.
Common Chicago mistakes
Confusing footnote and bibliography format — These are different. Footnotes put first name first and use commas; bibliographies put last name first and use periods. Mixing them up is one of the most common Chicago errors.
Using "p." or "pp." for page numbers — Chicago does not use p. or pp. for footnote page citations. Just write the number: (Smith 2021, 45) or ¹ Smith, Memory, 45.
Not shortening subsequent footnotes — After the first full citation, use the shortened form. Repeating the full citation for every reference is non-standard and clutters footnotes.
Using Author-Date when your subject expects Notes-Bibliography — If you are writing a history essay and using (Smith 2021, 45), your marker will notice. Check which system your department uses.
Missing bibliography entries — Every footnote must have a corresponding bibliography entry. Use the bibliography to double-check that nothing is missing.
For automatically formatted Chicago citations, use the Citation Reference Formatter. For other styles, see the MLA Guide, APA Guide, and Harvard Guide.
Frequently asked questions
What is Chicago referencing?
Chicago style is a citation system published by the University of Chicago Press. Its 17th edition (2017) offers two systems: Notes-Bibliography (NB), used in history, literature, and arts, which uses footnotes or endnotes and a bibliography; and Author-Date (AD), used in social sciences and sciences, which uses in-text parenthetical citations (Author Year) and a reference list. Always check which system your department requires.
What is the difference between Chicago and Turabian?
Turabian is a student adaptation of Chicago style. Kate L. Turabian's A Manual for Writers (now in its 9th edition) simplifies and adapts the full Chicago Manual of Style for student use. The citation formats are essentially identical; Turabian adds guidance specifically for student papers (title pages, margins, formatting). Most departments that specify 'Turabian' accept standard Chicago citations.
How do Chicago footnotes work?
In the Notes-Bibliography system, every cited source appears as a superscript number in the text. The same number appears at the bottom of the page (footnote) or at the end of the document (endnote) with the full citation. Subsequent citations of the same source are shortened: after the first full footnote, later references use just the author's last name, a short title, and page number. The bibliography at the end of the essay lists full details of all sources.
What is the difference between Chicago NB and Author-Date?
Notes-Bibliography uses footnotes (Author, Title, page) and a bibliography at the end. Author-Date uses in-text parenthetical citations (Author Year, page) like APA and a reference list at the end. NB is standard in humanities (history, literature, philosophy); Author-Date is standard in natural and social sciences. The reference list formatting in both systems is similar; the difference is how in-text references appear.
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