Chicago author-date style cites sources in the text with the author's surname and year, such as (Wanjiru 2023, 45), and lists full details in a reference list at the end. It is the Chicago system most used in the sciences and social sciences.
The Chicago Manual of Style is now in its 18th edition, published in 2024. This guide follows the 18th edition and notes where it differs from the 17th, since some courses still use the older rules.
Chicago Author-Date in Brief
- In text: (Author Year) or (Author Year, page), with no comma between author and year.
- Two authors: (Wanjiru and Patel 2023), using "and", not an ampersand.
- Reference list: titled "References", alphabetical by surname, with hanging indents.
- Year position: straight after the author's name in each entry.
Author-Date or Notes and Bibliography?
Chicago offers two citation systems. Your tutor or department decides which one you use, and you should not mix them within a paper.
| Feature | Author-date | Notes and bibliography |
|---|---|---|
| In-text form | (Author Year, page) | Superscript note number |
| Full details | Reference list | Footnotes or endnotes, plus a bibliography |
| Common subjects | Sciences and social sciences | History, literature and the arts |
In-Text Citations
Place the citation just before the punctuation at the end of the clause or sentence it supports. Add a page number whenever you quote or refer to a specific passage.
One author: (Wanjiru 2023)
With a page number: (Wanjiru 2023, 45)
Author named in the sentence: Wanjiru (2023, 45) argues that ...
Two authors: (Wanjiru and Patel 2023)
Three or more authors (18th edition): (Wanjiru et al. 2023)
Two sources at once: (Wanjiru 2023; Osei 2021)
Same author, same year: (Osei 2021a, 2021b)
Organizations, No Author and Secondary Sources
When an organization is the author, use its name: (World Health Organization 2023). When there is no author, start the reference list entry with the title and use a shortened title in the text. If you only read a source quoted in another work, cite the work you actually read and mention the original in your sentence.
The missing comma between author and year is the detail most often wrong in student papers, especially for writers used to APA. A comma does separate the year from the page number.
Reference List Rules
- Title the list "References" and start it on a new page.
- Order entries alphabetically by the first author's surname.
- Invert the first author's name only: Wanjiru, Grace, and Ravi Patel.
- Use a hanging indent for the second and later lines of each entry.
- Use headline-style capitalization for titles in English.
- Put article and chapter titles in quotation marks; italicize book and journal titles.
- Include a DOI as a URL when one exists.
Reference List Examples
The examples below use illustrative sources. Notice where the year sits and how volume, issue and pages are punctuated.
Journal article: Wanjiru, Grace, and Ravi Patel. 2023. "Peer Mentoring and Retention in First-Year Nursing Programs." Journal of Nursing Education Research 18 (2): 112–27. https://doi.org/10.1234/jner.2023.0112.
In text: (Wanjiru and Patel 2023, 115)
Book: Osei, Kwame. 2021. Cities in Transition: Housing and Migration in West Africa. Routledge.
In text: (Osei 2021, 88)
Chapter in an edited book: Mendes, Laura. 2022. "Measuring Belonging in Higher Education." In Student Wellbeing: Research and Practice, edited by Anna Clarke and Tomás Ruiz, 41–60. Bloomsbury Academic.
In text: (Mendes 2022, 45)
Web page: World Health Organization. 2023. "Adolescent Mental Health." October 17, 2023. https://www.who.int/news-room/fact-sheets/detail/adolescent-mental-health.
In text: (World Health Organization 2023)
For a web page with no publication or revision date, use "n.d." in place of the year and add an access date to the reference list entry.
What Changed in the 18th Edition
| Rule | 17th edition | 18th edition |
|---|---|---|
| In-text citation, three authors | List all three names | First author followed by et al. |
| Place of publication for books | Included before the publisher | No longer required |
If your course still uses the 17th edition, include the place of publication (for example, "London: Routledge") and name up to three authors in the text. Check your guidelines before choosing.
Common Mistakes
- Adding a comma between author and year: write (Osei 2021), not (Osei, 2021).
- Using "&" instead of "and" in citations and references.
- Putting the year at the end of the entry, as in notes and bibliography.
- Writing article titles in sentence case without quotation marks, as in APA.
- Leaving out page numbers for quotations.
- Mixing author-date citations with footnote citations in one paper.
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Frequently Asked Questions
A Chicago citation system that uses (Author Year, page) in the text and a reference list at the end, common in the sciences and social sciences.
No. Write (Osei 2021). A comma separates the year from a page number: (Osei 2021, 88).
In the 18th edition, use the first author's surname and et al.: (Wanjiru et al. 2023). The 17th edition named up to three authors.
Not in the 18th edition. The 17th edition included it before the publisher name.
"References". It is ordered alphabetically by the first author's surname.
Use "n.d." in place of the year, such as (World Health Organization n.d.), and add an access date to web sources.
Chicago author-date has no comma between author and year, uses "and" rather than an ampersand, and puts article titles in quotation marks with headline-style capitals.
Not for citations. You may still use occasional footnotes for comments, but source citations should follow one system.