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U.S. History Research

U.S. History Resources in the UML Library

How Do You Know Which Chicago Style to Use?

Chicago-style source citations come in two types:

notes and bibliography

To determine which system to follow the best first step is to check with your professor. However, there are some general rules of thumb.

From the Chicago Manual of Style website:

"The notes and bibliography system is preferred by many working in the humanities—including literature, history, and the arts. In this system, sources are cited in numbered footnotes or endnotes. Each note corresponds to a raised (superscript) number in the text. Sources are also usually listed in a separate bibliography. The notes and bibliography system can accommodate a wide variety of sources, including unusual ones that don’t fit neatly into the author-date system.

The author-date system is more common in the sciences and social sciences. In this system, sources are briefly cited in the text, usually in parentheses, by author’s last name and year of publication. Each in-text citation matches up with an entry in a reference list, where full bibliographic information is provided."




General Rule for the Notes & Bibliography Style

The Notes & Bibliography style is most often used by scholars in the humanities, e.g. history, literature, the arts.

 Place citations in notes either at the end of the page (footnotes) or at the end of the paper (endnotes).
 List all sources at the end of your paper on a new page entitled "Bibliography."
 Alphabetize the bibliography by author's last name, or by title if a work's author is unknown.

For typographic requirements of Chicago Style, ( margins, spacing, page numbering, etc.) please watch this Youtube video  which sets out a very clear description, with examples, of how to do this.

If you cannot access the above video, you can watch it here

Using Author-Date Style

Author-Date  style is a more concise format. It is usually used by scholars in the sciences and social sciences.

♦ Provide brief parenthetical citations within the paper (usually the author's last name and publication date).
♦ List full citations at the end of the work in a "Reference List."


It is often sufficient simply to describe web pages and other website content in the text (“As of May 1, 2017, Yale’s home page listed . . .”). If a more formal citation is needed, it may be styled like the examples below. For a source that does not list a date of publication or revision, use n.d. (for “no date”) in place of the year and include an access date.

Reference List Entries (in alphabetical order)

Bouman, Katie. 2016. “How to Take a Picture of a Black Hole.” Filmed November 2016 at TEDxBeaconStreet, Brookline, MA. Video, 12:51.

Google. 2017. “Privacy Policy.” Privacy & Terms. Last modified April 17, 2017.

Yale University. n.d. “About Yale: Yale Facts.” Accessed May 1, 2017.

In-text Citations

(Bouman 2016)

(Google 2017)

(Yale University n.d.)

For more examples, see 15.50–52 in The Chicago Manual of Style. For multimedia, including live performances, see 15.57.

Social Media

Citations of content shared through social media can usually be limited to the text (as in the first example below). If a more formal citation is needed, a reference list entry may be appropriate. In place of a title, quote up to the first 160 characters of the post. Comments are cited in reference to the original post.


Conan O’Brien’s tweet was characteristically deadpan: “In honor of Earth Day, I’m recycling my tweets” (@ConanOBrien, April 22, 2015).

Reference List Entries (in alphabetical order)

Chicago Manual of Style. “Is the world ready for singular they? We thought so back in 1993.” Facebook, April 17, 2015.

Souza, Pete (@petesouza). 2016. “President Obama bids farewell to President Xi of China at the conclusion of the Nuclear Security Summit.” Instagram photo, April 1, 2016.

In-text Citations

(Chicago Manual of Style 2015)

(Souza 2016)

(Michele Truty, April 17, 2015, 1:09 p.m., comment on Chicago Manual of Style 2015)