Chicago Author-Date Style | A Complete Guide to Citing Sources

The Chicago Manual of Style provides guidelines for two styles of source citation: notes and bibliography and author-date. Author-date style is the preferred option in the sciences and social sciences.

In author-date style, an in-text citation consists of the author’s name, the publication year, and (if relevant) a page number. Each citation must correspond to an entry in the reference list at the end of your paper, where you give full details of the source.

Using author-date in-text citations

In Chicago author-date style, you cite sources in parentheses in the text. The citation includes the author’s last name followed by the year of publication, with no punctuation in between:

(Smith 2012)

If you refer to a specific part of the text (particularly when quoting or paraphrasing), you should also add a page number or page range to direct the reader to the relevant passage. The page number appears after a comma and the first and last page are separated by an en dash.

(Smith 2012, 21–22)

Placement of in-text citations

A citation usually appears at the end of the relevant clause, sentence or quotation, before any concluding punctuation. If multiple citations are needed at the same point, they should appear in the same set of parentheses separated by a semicolon:

Previous researchers have argued that the evidence is insufficient to confirm a correlation (Smith 2012; Johnson 2015), but new evidence suggests this consensus may be mistaken (McDonald 2018).

If the researcher’s name is already mentioned in the text, the citation should appear straight after it and include only the date. If quoting, add a page number directly after the quote:

Smith (2012) argues that there is reason to believe this method has “great potential” (31). However, Johnson’s (2015) experiment fails to bear out this assertion.

Creating a reference list

The reference list appears at the end of your paper, and provides more detailed information about the sources you cited.

Each entry in the reference list also begins with the author’s last name and the publication date, so that your reader can easily find any source they encounter in the text:

Smith, James. 2012. Example Book. New York: Norton.

Your reference list is usually titled “References” or “Works Cited.” It is alphabetized by author last name. It is single-spaced, unlike the main text, but a blank line is left between entries.

Entries which extend onto more than one line have a “hanging indent,” which means the second and any subsequent lines are indented:

Garcia Márquez, Gabriel. 1988. Love in the Time of Cholera. Translated by Edith Grossman. London: Cape.

Below is an example of what a typical reference list looks like:

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Format of reference list entries

The format of the entry varies somewhat according to what type of source you’re citing. Examples for various source types are given below.

Book citation

Book citations include the title in italics, the place of publication and the publisher. If the book gives an edition on the title page, include this. Add the names of any editors and translators, and add a URL, DOI or e-book format if you consulted a digital version.

Book chapter citation

To cite a chapter from an edited collection, include the chapter title in quotation marks, the page range where the chapter appears, and the editor(s) of the book.

Journal article citation

Journal article entries include the volume and issue number, as well as a more specific publication date and a page range showing where the article appears in the journal. If accessed online, add a digital object identifier (DOI) or a URL.

Website citation

For web pages and online articles, put the page or article title in quotation marks, followed by the name of the website. If there is no publication date, replace the year with “n.d.” and give the date on which you accessed the page.

Variations on the format of Chicago author-date citations

The format of in-text citations and reference list entries can vary to accommodate circumstances like multiple authors, multiple publications by the same author in one year, and missing information.

Citing a source with multiple authors

When there are multiple authors, list their names in the same order as they appear in the source.

When a source has two or three authors, include the names of all the authors in your in-text citation. For sources with four or more authors, use the name of the first author followed by “et al.”

In the reference list, up to ten authors are listed. Alphabetize based on the first author’s last name. The other names are not inverted:

Gmuca, Natalia V., Linnea E. Pearson, Jennifer M. Burns, and Heather E. M. Liwanag. 2015. “The Fat and the Furriest: Morphological Changes in Harp Seal Fur with Ontogeny.” Physiological and Biochemical Zoology 88, no. 2 (March/April): 158–66.

In the case of a source with eleven or more authors, list the first seven in the reference list, followed by “et al.”

Citing multiple sources with the same author and year

If you cite multiple sources by the same author that were published in the same year, it’s important to use another identifier to distinguish between them in the text.

In cases like this, list the sources in alphabetical order by title in your reference list, and add a letter after the year of each one: a, b, c, et cetera.

List the same letters after the in-text citations—which may appear in the text in a different order:

(Smith 2012b)

(Smith 2012a)

Citing sources with missing information

Sometimes not all the information required for a citation will be available.

If you need to cite a source with no publication date, write “n.d.” (“no date”) in place of the date in your in-text citation and in your reference list:

(Smith n.d.)

Smith, James. n.d. Example Book. New York: Norton.

If you need to cite a source with no author, there are a couple of scenarios. If you’re dealing with a source issued by an organization without a specific author listed (for example, a press release or pamphlet), you can list the organization as the author:

(University of Glasgow 2019)

University of Glasgow. 2019. “Colombian River Guardians Rally Support in Scotland.” October 14, 2019. https://www.gla.ac.uk/news/headline_678538_en.html.

If this doesn’t work for your source, begin your reference list entry with the title instead, alphabetized according to the first word of the title (ignoring articles):

The Example Book: A Book of Examples. 2012. New York: Norton.

Here the entry would be alphabetized under “E”, not “T”, because the article is ignored for alphabetization.

For an in-text citation, use the title. If the title is longer than four words, use a shortened version of it starting with the first word (excluding articles):

(Example Book 2012)

Note that if a source is explicitly attributed to “Anonymous,” this word should simply be used as a name:

(Anonymous 2011)

Frequently asked questions about Chicago author-date style

When should I include page numbers in Chicago style citations?

Page numbers should be included in your Chicago in-text citations when:

• You’re quoting from the text.
• You’re paraphrasing a particular passage.
• You’re referring to information from a specific section.

When you’re referring to the overall argument or general content of a source, it’s unnecessary to include page numbers.

When should I use “et al.” in Chicago style citations?

When a source has four or more authors, your in-text citation or Chicago footnote should give only the first author’s name followed by “et al.” (Latin for “and others”). This makes your citations more concise.

In your bibliography or reference list, when a source has more than 10 authors, list the first seven followed by “et al.” Otherwise, list every author.

What is the difference between a Chicago reference list and a bibliography?

• A reference list is used with Chicago author-date citations.
• A bibliography is used with Chicago footnote citations.

Both present the exact same information; the only difference is the placement of the year in source citations:

• In a reference list entry, the publication year appears directly after the author’s name.
• In a bibliography entry, the year appears near the end of the entry (the exact placement depends on the source type).

There are also other types of bibliography that work as stand-alone texts, such as a Chicago annotated bibliography.

Do I have to include a bibliography or reference list?

In Chicago author-date style, your text must include a reference list. It appears at the end of your paper and gives full details of every source you cited.

In notes and bibliography style, you use Chicago style footnotes to cite sources; a bibliography is optional but recommended. If you don’t include one, be sure to use a full note for the first citation of each source.