Citation Styles

How often do I cite?

  • Remember: one citation at the end of a string of sentences or a paragraph cannot “cover” the entire section.
  • Cite a source the first time it is used in each paragraph.
  • Every sentence thereafter in the paragraph that uses information from this same source must contain either a signal phrase or a citation clearly indicating where the information came from.
    • Note: always use a citation (even if you also use a signal phrase) every time you quote material.

Footnote Placement in Sentence

Where in the sentence does my footnote go?

  • Single footnotes go at the end of a sentence, after the punctuation, like this.1
  • “If the sentence ends with a quotation, the quotation marks go outside the punctuation, then the footnote is placed after the quotation marks, like this.”2
  • Please do not insert any spaces before a footnote; please do put a space between a footnote and the beginning of the next sentence.

In the paragraph below, the reference numbers are highlighted in yellow and the signal phrases are highlighted in blue. Note that the second sentence is common knowledge, whereas the final sentence is clearly the opinion of the author. 

Red and yellow are the best colors with which to decorate your restaurant because they induce feelings of hunger.1 Consider popular fast-food chains, which often use red and yellow in their advertising and décor. According to Smith and Jones’ study,2 restaurant customers felt more energized in red and yellow environments, which encouraged them to order more food. The same study indicated that patrons felt relaxed in blue and purple environments, which encouraged them to “spend more time considering the the menu options and eat at a slower pace.”1 Although blue décor can give your restaurant a more casual, laid-back feel, Smith and Jones believe it encourages patrons to linger at their tables without ordering additional food or beverages.2 Accordingly, it is difficult to identify a popular chain restaurant that decorates with calmer hues.

 For more information, see the TPO's Citing Responsibly in Chicago Notes & Bibliography.

Difference between List of References and a Bibliography

A List of References includes all works cited in a text

A Bibliography lists all works cited and consulted

For papers, check with your professors for their preference. Thesis Processing prefers a List of References for the following: 

  • Thesis
  • Capstone project report
  • MBA report
  • Dissertation

Multiple Citations in a Single Sentence

When citing more than one source in a single sentence, there are two options:

  • Place a single footnote at the end of the sentence, outside the punctuation, and include all citations in this footnote, separated by semicolons. See CMS 14.57.
  • Place each footnote at the end of the clause containing the information it cites. See CMS 14.26.

Never place more than one footnote at the end of a sentence. See CMS 14.28.

Ibid. and Shortened Citations

Chicago prefers shorter citations, but ibid. is still allowed when the footnote is identical to the one right before it. See CMS 14.034Be consistent. Use either ibid. or shorter citations.

There are four forms of notes:

  • Full citation for first appearance
  • Short citations for subsequent appearances: Author, Title, page number.
  • Shorter citations contain only author and page number and appear directly after full or short citations until you change to another source. Use instead of ibid.
  • Ibid. (not preferred)

Example Footnotes List:

11. Toni Morrison, Beloved (New York: Vintage, 2004), 3.
12. Morrison, 18.
13. Morrison, 18.
14. Toni Morrison, Song of Solomon (New York: Vintage, 2004), 45.
15. Morrison, 47
16. Morrison, Beloved, 52.
17. Morrison, 55.
18. Morrison, Song of Solomon, 324–25.
19. Morrison, 238.
20. Morrison, 239.
21. Morrison, Song of Solomon, 240; Beloved, 32.
22. Morrison, Beloved, 33.
23. Morrison, 34.
24. FBI, “Stolen Memories.” [Full citation appeared in an earlier footnote, not shown here]
25. FBI.

Title Case and Sentence Case Difference

Title Case: To Capitalize or Not: A Brief Tutorial

Sentence case: To capitalize or not: A brief tutorial

When Do I Need to Add Page Numbers?

Always include page numbers in notes when available.

N: Michael PollanThe Omnivore’s Dilemma: A Natural History of Four Meals (New York: Penguin, 2006), 99–100.

S: Pollan, The Omnivore’s Dilemma, 100.

For book chapters, include page-number range in List of References/Bibliography.

B: Haynes, Peter. “Al-Qaeda, Oil Dependence, and U.S. Foreign Policy.” In Energy Security and Global Politics: The Militarization of Resource Management, edited by Daniel Moran and James A. Russell, 62–74. New York: Routledge, 2009.


  • Include a retrieval date if the source material has no date.
  • Always include a period at the end of the URL.

Et al.

  • Up to three authors:
    • In the Bibliography / List of References, include all of them
    • In the footnote, include all of them
    • In the text, include all of them
  • Four to ten authors:
    • In the Bibliography / List of References, include all of them
    • In the footnote, list only the first author, followed by et al.
    • In the text, list only the first author, followed by et al. (“and others”)
  • More than ten authors:
    • In the Bibliography / List of References, include only the first seven, followed by et al.
    • In the footnote, list only the first author, followed by et al.
    • In the text, list only the first author, followed by et al.

Secondary Sources

A secondary source is a source that cites some other work that you discuss in your text.

Whenever possible, consult primary sources and your sources’ sources yourself. Upon investigation of the primary source, you may find you disagree with the secondary source author’s analysis or methods. Only use secondary sources when the primary source is unavailable.

How to Incorporate Secondary Sources

The following passage incorporates a properly credited secondary source. The secondary source information is highlighted in yellow; the primary source information is highlighted in blue.

Walker describes data collected in 1999 by Miguel Roig that correlates students’ inadequate paraphrasing to poor reading comprehension. Citing Roig’s data, Walker explains that “students do in fact possess skills necessary for paraphrasing but … may be impeded from applying those skills when dealing with rigorous text”1

Note: Include  only  the  secondary  source  (the  source  you  consulted)  in  your  reference  list.