Chicago style citation comes from The Chicago Manual of Style and offers two systems: notes-bibliography, used mainly in history and the humanities, and author-date, used mainly in the sciences and social sciences.
The 18th edition was published in 2024, and many courses still use the 17th. This page covers both systems, with examples for the sources you will cite most and the points where the editions differ.
Which Chicago System to Use
Use notes-bibliography if your course is in history, literature, art or philosophy, or if your instructor asks for footnotes. Use author-date if your course is in the sciences or social sciences, or if you are asked for parenthetical citations with a reference list.
If your handbook does not say, ask. The two systems should never be mixed in one paper.
The Two Systems Compared
| Feature | Notes-bibliography | Author-date |
|---|---|---|
| In-text citation | Superscript number linked to a footnote or endnote | (Author Year, page) in parentheses |
| Source list | Bibliography | References |
| Position of year in list | Near the end of the entry | Straight after the author |
| Typical subjects | History, literature, arts | Sciences, social sciences |
Footnotes and Shortened Notes
In notes-bibliography, each citation is marked with a superscript number placed after the punctuation at the end of the clause. The number links to a footnote at the bottom of the page or an endnote at the end of the paper.
The first note for a source gives full details. Later notes for the same source use a shortened form: the author's surname, a short title of up to four words and the page.
Full note: 1. Peter Marsh, Empire and the Market Town (Leeds: Northgate Press, 2019), 47.
Shortened note: 2. Marsh, Empire and the Market Town, 52.
Both recent editions prefer shortened notes to "Ibid.". If your instructor still accepts "Ibid.", use it only for a source cited in the note immediately before.
Notes-Bibliography Examples
Book
Note: 1. Peter Marsh, Empire and the Market Town (Leeds: Northgate Press, 2019), 47.
Bibliography: Marsh, Peter. Empire and the Market Town. Leeds: Northgate Press, 2019.
Journal Article
Note: 3. Rosa M. Hale, "Ports, Credit and Kinship in the Eighteenth Century," Journal of Maritime History 14, no. 2 (2021): 91, https://doi.org/10.1000/xyz123.
Bibliography: Hale, Rosa M. "Ports, Credit and Kinship in the Eighteenth Century." Journal of Maritime History 14, no. 2 (2021): 88–107. https://doi.org/10.1000/xyz123.
Website
Note: 4. "The Town Charter of 1612," Borough Archive Project, last modified March 3, 2024, https://www.example.org/charter.
Bibliography: Borough Archive Project. "The Town Charter of 1612." Last modified March 3, 2024. https://www.example.org/charter.
Notice the differences: notes use commas and parentheses and put the first name first; bibliography entries invert the first author's name and use full stops between elements.
Author-Date Examples
Author-date places a short citation in parentheses in the text, with no comma between author and year, and a comma before the page.
In text: Credit networks depended on family ties (Hale 2021, 91).
Book reference: Marsh, Peter. 2019. Empire and the Market Town. Leeds: Northgate Press.
Journal reference: Hale, Rosa M. 2021. "Ports, Credit and Kinship in the Eighteenth Century." Journal of Maritime History 14 (2): 88–107. https://doi.org/10.1000/xyz123.
- Two authors: (Marsh and Hale 2020).
- Same author, same year: add a, b and so on: (Hale 2021a).
- No date: use "n.d." in place of the year.
17th and 18th Editions: What to Check
Most core patterns are the same in both editions. The main changes in the 18th edition that affect student papers are these.
- Place of publication: the 18th edition no longer requires the city for books, so "Northgate Press, 2019" is acceptable. Many courses on the 17th edition still expect it.
- Multiple authors in notes: the 17th edition uses the first author plus "et al." in notes for works with four or more authors; the 18th edition lowers this threshold.
- Shortened notes: the 18th edition continues to favor shortened notes over "Ibid.".
Follow the edition your course names. Where it does not name one, ask, and then stay consistent throughout.
Formatting the Bibliography
- Title the list "Bibliography" (notes-bibliography) or "References" (author-date).
- Arrange entries alphabetically by the first author's surname.
- Use a hanging indent of half an inch.
- Single-space within entries and leave a blank line between them, unless your instructor asks for double spacing.
- Italicize titles of books and journals; put article and chapter titles in quotation marks.
- Use headline-style capitalization for titles.
Common Chicago Mistakes
| Mistake | Fix |
|---|---|
| Mixing notes and author-date | Choose one system for the whole paper |
| Full note repeated every time | Use a shortened note after the first citation |
| Note numbers before punctuation | Place them after the full stop or comma |
| Bibliography with first name first | Invert the first author's name |
| Year in the wrong place for author-date | Put the year straight after the author |
| Mixing 17th and 18th edition rules | Pick one edition and apply it consistently |
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Frequently Asked Questions
Turabian is a student version of Chicago, adapted for papers, theses and dissertations. The citation rules are almost identical.
Either is acceptable in notes-bibliography. Footnotes are more common in student papers unless your instructor prefers endnotes.
Usually yes. Most instructors expect a bibliography with notes-bibliography, although Chicago allows full notes to stand alone in some cases.
Recent editions prefer shortened notes. Some instructors still accept "Ibid." for a source cited in the immediately preceding note.
After the punctuation at the end of the clause or sentence, except before a dash.
The edition your course names. The 18th edition is current, but many courses still use the 17th.
History usually uses notes-bibliography. Use author-date only if your instructor asks for it.
In notes-bibliography, start with the title. In author-date, use the title or the organization in place of the author.