Chicago Style Citations Explained: Notes-Bibliography vs Author-Date

Chicago style is one of the oldest and most detailed citation systems in academic writing. It’s maintained by the University of Chicago Press, currently in its 17th edition, and is the go-to format for history, some humanities disciplines, and certain social science departments.

The part that confuses most students: Chicago isn’t one system — it’s two. Understanding which one your professor wants is the first step.

The Two Chicago Systems

Notes-Bibliography (NB)

This is the system most people mean when they say “Chicago style.” It uses footnotes (or endnotes) plus a bibliography at the end of the paper.

• Used in: History, arts, literature, philosophy, religion
• How it works: You place a superscript number in the text.¹ The corresponding footnote at the bottom of the page gives the full citation. A bibliography at the end lists all sources alphabetically.

Author-Date (AD)

This system looks more like APA or Harvard — parenthetical citations in the text that point to a reference list.

• Used in: Social sciences, natural sciences, some business courses
• How it works: You cite as (Smith 2024, 45) in the text and list full references at the end.

Which should you use? Check your assignment brief. If it says “Chicago” without specifying, and you’re in a history or humanities course, it almost certainly means Notes-Bibliography. If you’re in the social sciences, it likely means Author-Date. When in doubt, ask your professor.

Notes-Bibliography: How It Works

Footnotes

When you reference a source, place a superscript number at the end of the relevant sentence. The footnote appears at the bottom of that page.

First citation of a source (full note):

¹ John Smith, The French Revolution: A New History (Oxford: Oxford University Press, 2023), 145.

Subsequent citations of the same source (short note):

² Smith, The French Revolution, 152.

Consecutive citations of the same source:

³ Ibid., 160.

(“Ibid.” means “in the same place” — use it only when the immediately preceding footnote is the same source.)

Footnote Examples by Source Type

Book (single author):

¹ Sarah Williams, Modern European History (Cambridge: Cambridge University Press, 2024), 78.

Book (two authors):

² John Smith and Mary Jones, Collaborative Histories (London: Penguin, 2023), 34.

Book (three or more authors):

³ John Smith et al., Global Perspectives on War (New York: Routledge, 2024), 201.

Journal article:

⁴ Emma Taylor, “Revisiting the Industrial Revolution,” Historical Review 45, no. 2 (2023): 112-128.

Website:

⁵ David Brown, “Understanding Primary Sources,” Research Skills Hub, January 15, 2025, www.researchskillshub.com/primary-sources.

Chapter in an edited book:

⁶ Robert Green, “The Role of Archives,” in The Historian’s Toolkit, ed. Laura White (Chicago: University of Chicago Press, 2024), 56-78.

The Bibliography

The bibliography appears at the end of your paper and lists every source in alphabetical order by author surname. The formatting is slightly different from the footnote — the author’s name is inverted (surname first), and the punctuation changes.

Book:

Smith, John. The French Revolution: A New History. Oxford: Oxford University Press, 2023.

Journal article:

Taylor, Emma. “Revisiting the Industrial Revolution.” Historical Review 45, no. 2 (2023): 112-128.

Website:

Brown, David. “Understanding Primary Sources.” Research Skills Hub. January 15, 2025. www.researchskillshub.com/primary-sources.

Note the differences from the footnote: surname comes first, periods replace commas between major elements, and no specific page number is listed (the bibliography covers the whole source, not a specific page).

Author-Date: How It Works

If you’ve used APA before, Chicago Author-Date will feel familiar.

In-Text Citations

• One author: (Smith 2024, 45)
• Two authors: (Smith and Jones 2023, 34)
• Three or more authors: (Smith et al. 2024, 201)
• No page number: (Smith 2024)
• Author named in sentence: Smith (2024, 45) argues that…

Note there’s no comma between the author and year — this differs from APA, which uses (Smith, 2024, p. 45).

Reference List

The reference list at the end uses a format similar to the bibliography but with the year moved to a prominent position after the author name:

Book:

Smith, John. 2023. The French Revolution: A New History. Oxford: Oxford University Press.

Journal article:

Taylor, Emma. 2023. “Revisiting the Industrial Revolution.” Historical Review 45 (2): 112-128.

Website:

Brown, David. 2025. “Understanding Primary Sources.” Research Skills Hub. January 15, 2025. www.researchskillshub.com/primary-sources.

What About Turabian?

You’ll sometimes see “Turabian” listed as a citation style. Turabian is a simplified version of Chicago, written by Kate Turabian specifically for students. It follows the same two systems (Notes-Bibliography and Author-Date) with nearly identical formatting rules but leaves out some of the more advanced publishing details from the full Chicago Manual.

If your assignment says “Turabian,” follow the same rules in this guide. The differences are minimal for undergraduate work.

Notes-Bibliography vs Author-Date: Quick Comparison

Feature	Notes-Bibliography	Author-Date
In-text format	Superscript footnote numbers	(Author Year, Page)
Bottom of page	Footnotes with full details	Nothing
End of paper	Bibliography	Reference List
Common disciplines	History, arts, philosophy	Social sciences
First citation	Full footnote	Same as all citations
Repeat citations	Shortened footnote	Same as all citations

Common Chicago Mistakes

1. Mixing the two systems — using footnotes with a reference list, or author-date with a bibliography. Each system has its own end-matter format.
2. Forgetting short notes — after the first full footnote for a source, subsequent citations should use the shortened form, not the full note again.
3. Overusing “Ibid.” — only use it when the immediately preceding footnote is the exact same source. If another source appears in between, use the short note form instead.
4. Wrong punctuation in the bibliography — footnotes use commas between elements; bibliography entries use periods. Students often copy the footnote format into the bibliography.
5. Missing the bibliography entirely — footnotes don’t replace the bibliography. You need both.
6. Confusing bibliography and reference list — Notes-Bibliography uses a “Bibliography”; Author-Date uses a “Reference List.” The terms aren’t interchangeable.

Let RefFinder Format Your Chicago Citations

Chicago is arguably the most complex citation style because of the dual system, the footnote/bibliography distinction, and the many punctuation rules. Formatting a 15-source history essay by hand means writing each source three different ways (full note, short note, bibliography entry).

RefFinder handles all of this automatically. Paste your essay, select Chicago (Notes-Bibliography or Author-Date), and get correctly formatted citations ready to drop into your paper.

Try RefFinder free — your footnotes and bibliography, done in seconds.