The Chicago referencing style is widely used across the humanities, including history, literature, philosophy, and the arts. The guidelines are maintained by the University of Chicago Press and published in the Chicago Manual of Style. Chicago uses a footnote and bibliography system, where sources are cited using a superscript number¹ linked to a full reference in a footnote at the bottom of the page.
Chicago In-text Citation Examples
In Chicago style, you place a superscript number in your text at the point where a source is used. The corresponding footnote includes full source details. The numbers run consecutively throughout your document—you don’t restart numbering on a new page.
Superscript citation at the end of a sentence and footnote at the bottom of the page
Recent research shows that digital archives have transformed how historians access primary documents.1 These patterns mirror earlier trends observed in large-scale digitisation projects.2
Footnotes
1. Maria Clarke, “Digital Archives and Historical Practice,” Journal of Digital History 14, no. 2 (2019): 88.
2. James Rowe, “New Approaches to Online Collections,” Historical Methods 22, no. 1 (2015): 15.
Citing the Same Source More than Once
Even if you cite the same source more than once, it still receives a new citation number each time. The first citation uses a full footnote, while later citations use a shortened note.
We cited the same source twice. The first footnote includes the full reference, while the second uses a shortened version for repeat citations.
Digital archives have made rare manuscripts far more accessible.1 Historians also note that user engagement with these collections continues to rise.2
Footnotes
1. Clarke, “Digital Archives and Historical Practice,” 88. (Full note)
2. Clarke, “Digital Archives,” 88. (Short note)
Citing Multiple Sources in Chicago Style
When multiple sources support the same statement, use one superscript number and combine all sources in a single footnote, separated by semicolons.
✖ Incorrect method — do NOT use multiple superscripts
Recent studies show that digital archives significantly improve access to historical documents.1,2
Footnotes
1. Maria Clarke, “Digital Archives and Historical Practice,” Journal of Digital History 14, no. 2 (2019): 88.
2. James Rowe, “New Approaches to Online Collections,” Historical Methods 22, no. 1 (2015): 15.
✔ Correct method — use one superscript and combine all sources into one footnote
Recent studies show that digital archives significantly improve access to historical documents.1
Footnotes
1. Maria Clarke, “Digital Archives and Historical Practice,” Journal of Digital History 14, no. 2 (2019): 88; James Rowe, “New Approaches to Online Collections,” Historical Methods 22, no. 1 (2015): 15.
Secondary References in Chicago Style
Secondary referencing is used when you discuss information that you found quoted or summarised in another author’s work but were unable to access the original source. In Chicago style, you mention the original author in your sentence but cite the source you actually read in the footnote. Only the source you consulted appears in the bibliography.
Secondary referencing should be used sparingly and only when the original material is genuinely inaccessible.
Let’s say Turner (2020) discusses findings from a study by Williams (2012), and you cannot access Williams’s original research.
In-text citation
Williams’s 2012 analysis of digital archives is summarised in Turner’s study.1Footnotes
1. Paul Turner, “New Approaches to Digital Preservation,” Journal of Archival Studies 11, no. 1 (2020): 44.Bibliography
Turner, Paul. “New Approaches to Digital Preservation.” Journal of Archival Studies 11, no. 1 (2020): 40–55.(Note: Williams (2012) does not appear in the bibliography, because you did not read the original work.)
Direct Quotes in Chicago Style
Direct quotes must appear within double quotation marks, and the footnote must include the page number where the quote appears.
Direct quote from a paper enclosed in double quotes and page number mentioned in the footnote
As Brown explains, “Digital humanities tools allow researchers to analyse texts at unprecedented scale.”4
Footnotes
1. Laura Brown, “Text Mining in the Humanities,” Digital Scholarship Review 7, no. 3 (2020): 112.
Citing AI Tools like ChatGPT in Chicago Style
Chicago does not yet have official rules for citing generative AI tools, but most institutions recommend treating AI-generated responses as personal communication, since the content cannot be retrieved by others. When you refer to the tool itself (rather than its output), you may cite it as a website or software platform.
Citing ChatGPT as personal communication (Use this when you include text generated by ChatGPT)
In-text citation
Historians can now process large volumes of digitised material far more efficiently.1Footnotes
1. ChatGPT, response to the prompt “Explain how digital archives improve research accessibility,” March 18, 2025.Bibliography
Not included in bibliography since the content cannot be retrieved by others
Citing ChatGPT as Software (when discussing the tool itself)
In-text citation
ChatGPT is widely used to generate quick explanations for complex topics.2Footnotes
2. OpenAI, ChatGPT, accessed March 18, 2025, https://chat.openai.com/.Bibliography
OpenAI. ChatGPT. Accessed March 18, 2025. https://chat.openai.com/.
⚠️ Important Note on Citing AI Tools
Guidelines for citing AI tools like ChatGPT vary widely between universities, and many institutions are still updating their policies. Always check your department’s or university’s official referencing guide to ensure you follow the correct requirements.
Reference List (Chicago Bibliography)
Your reference list, titled Bibliography, appears at the end of your document.
It should:
- List all sources alphabetically by the author’s surname
- Use hanging indent formatting (first line left-aligned, subsequent lines indented)
For a clearer understanding of how different sources should be formatted, here are sample Chicago references for common source types. For further information, read this blog.
References Formatted in Chicago Style
Journal article
Clarke, Maria. “Digital Archives and Historical Practice.” Journal of Digital History 14, no. 2 (2019): 80–95.Book
Lopez, Samuel. Telemedicine in Modern Healthcare. London: MedTech Press, 2021.Website
HealthTech Insights. “How AI Is Improving Patient Triage.” Last modified 2023. https://www.healthtechinsights.org/triage.Conference paper
Wong, Lucas, and Megan Carter. “Integrating Mobile Diagnostics into Emergency Services.”
In Proceedings of the Digital Health Technology Conference, 122–130. London: Heritage Press, 2021.Thesis / Dissertation
Rahman, Sarah. “Adaptive Learning Algorithms for Digital Tutoring Systems.” PhD diss., University of Manchester, 2023.Report
International Health Board. Global Telehealth Outlook 2023. Geneva: IHB Publications, 2023.YouTube Video
MedTech Channel. “How Digital Tools Support Patient Care.” YouTube video, 6:12, posted February 10, 2024.
https://www.youtube.com/watch?v=example123.Dataset
HealthData Lab. Patient Activity Records, 2019–2023. HealthData Repository, 2023.
https://www.healthdata.org/patient-activity.Legislation
United Kingdom. Digital Health Act 2021. c.15.
Summary
The Chicago referencing style may appear detailed at first, but once you understand the basics—superscript numbers, full footnotes, short footnotes, and a properly formatted bibliography—it becomes straightforward to use. Keep your numbering consistent, provide full notes the first time a source appears, and use short notes for repeat citations.
If you still have questions about Chicago style, feel free to check our upcoming FAQs section or explore our other blogs on plagiarism, paraphrasing, and ai detection.
