Chicago Style Explained: Notes-Bibliography vs Author-Date
Chicago is really two systems in one manual. Learn when historians use footnotes, when scientists use author-date, and how to format both.
The Chicago Manual of Style (18th edition) is unusual: it contains two complete citation systems. Notes–Bibliography (NB) uses numbered footnotes or endnotes and dominates history, art history, and theology. Author–Date works like APA/Harvard and serves the sciences and social sciences. Your first job is knowing which one your department expects.
System 1: Notes–Bibliography
A superscript number in the text points to a footnote at the bottom of the page. The first note for a source is full. Later notes are shortened.
First footnote:
1. Jared Diamond, Guns, Germs, and Steel: The Fates of Human Societies (New York: W. W. Norton, 1997), 213.
Subsequent note:
2. Diamond, Guns, Germs, 215.
Bibliography entry:
Diamond, Jared. Guns, Germs, and Steel: The Fates of Human Societies. New York: W. W. Norton, 1997.
Note the inversions: footnotes use first-name-first and commas. The bibliography uses surname-first and periods. "Ibid." is now discouraged by Chicago itself, use the shortened form instead.
Journal Article in NB
3. Joan W. Scott, "Gender: A Useful Category of Historical Analysis," American Historical Review 91, no. 5 (1986): 1067.
Scott, Joan W. "Gender: A Useful Category of Historical Analysis." American Historical Review 91, no. 5 (1986): 1053–75.
System 2: Author–Date
Citations sit in the text, (Diamond 1997, 213), and point to a reference list where the year moves up front:
Diamond, Jared. 1997. Guns, Germs, and Steel: The Fates of Human Societies. New York: W. W. Norton.
Everything else (capitalisation, punctuation of titles) mirrors the NB bibliography form. If you know one system, you are 80% of the way to the other.
Which System When?
- NB suits disciplines that cite archival material, primary documents, and need discursive footnotes for commentary. A footnote can hold a mini-argument. An author-date bracket cannot.
- Author–Date suits empirical work where the currency of a finding (its year) matters at a glance.
Formatting Conventions
- Title case for all titles ("A Useful Category of Historical Analysis"), unlike APA's sentence case.
- Footnote numbers go after punctuation, at the end of the clause or sentence.
- Bibliography: alphabetical, hanging indent. A 3-em dash may replace a repeated author's name in successive entries.
- Page ranges compress per Chicago's rules: 1053–75, not 1053–1075.
Choosing Between the Two Systems
Chicago's own quick guide describes Notes and Bibliography as its "oldest and most flexible" system, "preferred by many working in the humanities, including literature, history, and the arts". Author-Date, it says, "is preferred by many in the sciences and social sciences". On choosing, the guide is refreshingly plain: most authors use the system used by others in their field or required by their publisher, and students should consult their instructor before selecting one.
In other words, this is rarely your decision. Ask before you start, because converting a finished paper between the two is tedious.
| Notes and Bibliography | Author-Date | |
|---|---|---|
| In-text | Superscript number | (Diamond 1997, 213) |
| Full citation lives | In the footnote | In the reference list |
| End list called | Bibliography | References |
| Year position | Late, in parentheses | Immediately after the author |
| Can hold commentary | Yes, footnotes take discursive text | No |
| Typical fields | History, art history, theology, literature | Sciences, social sciences |
Notes Versus Bibliography Form
The same source formatted three ways is the fastest way to internalise the differences. Every difference below is deliberate and marked.
| Form | Diamond example |
|---|---|
| First footnote | 1. Jared Diamond, Guns, Germs, and Steel (New York: W. W. Norton, 1997), 213. |
| Shortened note | 2. Diamond, Guns, Germs, 215. |
| Bibliography | Diamond, Jared. Guns, Germs, and Steel. New York: W. W. Norton, 1997. |
| Author-date reference | Diamond, Jared. 1997. Guns, Germs, and Steel. New York: W. W. Norton. |
Three differences do most of the work. Footnotes run first name first, the bibliography inverts to surname first. Footnotes separate elements with commas, the bibliography uses full stops. Footnotes put publication details in parentheses, the bibliography does not.
Formats by Source Type
| Source | Note form |
|---|---|
| Book | 1. Jared Diamond, Guns, Germs, and Steel (New York: W. W. Norton, 1997), 213. |
| Chapter | 2. Anne Marsh, "Photography and Memory," in Visual Cultures, ed. Peter Hall (Chicago: University of Chicago Press, 2019), 88. |
| Journal article | 3. Joan W. Scott, "Gender: A Useful Category of Historical Analysis," American Historical Review 91, no. 5 (1986): 1067. |
| Website | 4. "About the Collection," British Library, accessed August 11, 2026, https://www.bl.uk/collections. |
| Archival document | 5. Letter from A. Hughes to J. Bell, March 4, 1912, Hughes Papers, box 4, folder 7, Manchester Central Library. |
| Thesis | 6. Maria Alvarez, "Urban Housing Reform" (PhD diss., University of Manchester, 2023), 142. |
The archival format is why history departments favour Notes and Bibliography. Manuscript material carries box and folder numbers that no author-date bracket can accommodate.
Formatting Conventions
- Title case for all titles, unlike APA's sentence case.
- Footnote numbers after punctuation, at the end of the clause or sentence.
- Bibliography alphabetical with a hanging indent. A 3-em dash may replace a repeated author name in successive entries.
- Compressed page ranges: 1053-75, not 1053-1075.
- "Ibid." is now discouraged by Chicago itself. Use the shortened note form instead.
Common Errors and Fixes
| Error | Fix |
|---|---|
| Footnotes formatted like bibliography entries | Notes use commas and first-name-first. The bibliography uses full stops and surname-first |
| Full citation in every footnote | Shorten after the first: Diamond, Guns, Germs, 215 |
| Using "Ibid." | Chicago now discourages it. Use the shortened form |
| Mixing both systems in one paper | Pick one at the outset and apply it throughout |
| Sentence case titles | Chicago uses title case |
| Uncompressed page ranges | 1053-75, not 1053-1075 |
Country and Discipline Notes
- United States: Chicago is the dominant style in history and widely used across the humanities.
- UK and Ireland: less common than Harvard, but standard in some history and theology departments. MHRA is an alternative in literature.
- Australia and New Zealand: used in history and art history, often alongside a local Harvard variant.
- India: less common, though it appears in humanities postgraduate work.
- Turabian: a student-focused adaptation of Chicago. If your brief says Turabian, expect Chicago's structure with simplified rules.
Shortened Notes Done Properly
Chicago's shortened form carries three elements: author surname, a short title, and the pinpoint. Nothing else.
- Full: 1. Jared Diamond, Guns, Germs, and Steel (New York: W. W. Norton, 1997), 213.
- Shortened: 2. Diamond, Guns, Germs, 215.
- Not: 2. Diamond, Guns, Germs, and Steel (New York: W. W. Norton, 1997), 215.
Shorten the title to four words or fewer where the meaning survives. Where two sources by the same author could be confused, keep enough of each title to distinguish them.
Where Ethical Support Fits
Checking whether your notes and bibliography follow the different conventions is legitimate, and it is exactly the kind of mechanical error a proofreader catches quickly. What stays yours is the argument the footnotes support, and in history that includes deciding which archival sources matter.
Frequently Asked Questions
How do I cite an interview or personal communication?
Chicago usually keeps these in a note rather than the bibliography, giving the interviewee, the interviewer, the format and the date.
Do the two systems share the same bibliography?
Almost. The entries carry the same information, but author-date moves the year forward to sit immediately after the author. Everything else, including title case and punctuation, matches.
Which Chicago system should I use?
Ask your instructor. Chicago's own guidance says students should consult their instructor before choosing, and most fields have a settled convention.
Footnotes or endnotes?
Either is acceptable to Chicago. Your department usually specifies, and footnotes are more common in student work because they are easier to read.
Do I need a bibliography if every citation is in a footnote?
Usually yes for extended work. Check the brief, since some short essays require notes only.
Can a footnote contain discussion rather than a citation?
Yes, and this is one of the system's strengths. A note can carry a qualification or a brief aside that would derail the main text.
What is the 3-em dash for?
It replaces a repeated author name across consecutive bibliography entries, so the same author is not retyped for each work.
Is Chicago 18th edition very different from the 17th?
The core systems are unchanged. Differences are mostly in the treatment of online and audiovisual sources, so an older guide will still be broadly right for books and articles.
Your Next Step Today
Look at your second footnote citing a source you already cited. If it repeats the full citation, shorten it. That single habit accounts for a large share of Chicago formatting errors in student work.
Trusted Sources
- The Chicago Manual of Style, Citation Quick Guide, 18th edition, source of the descriptions of both systems and the advice to consult your instructor. Accessed 11 August 2026.
- Purdue OWL, Chicago Manual of Style formatting and style guide, worked student examples. Accessed 11 August 2026.
- MLA Style Center, for comparison where a humanities course requires MLA instead. Accessed 11 August 2026.
- APA Style, Common Reference Examples Guide, for comparison with Chicago author-date. Accessed 11 August 2026.
Departments sometimes specify Turabian or a local adaptation. Where this guide and your handbook differ, follow the handbook.
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