How to Cite Sources in Chicago Author-Date Style

The author-date system is the second of two citation methods described in the Chicago Manual of Style (18th edition). While the notes-bibliography system dominates in history and the humanities, the author-date system is the standard in the natural sciences, social sciences, and many areas of business and education. It works the same way most scientists are already familiar with: a brief parenthetical reference in the text points the reader to a full entry in an alphabetical reference list at the end of the paper.

This guide walks through the mechanics of the system - constructing in-text citations, handling special cases like multiple authors or missing dates, building the reference list, and understanding how Chicago author-date compares to APA style. If you prefer to generate your citations automatically, the AllCitations Chicago Author-Date generator can produce correctly formatted entries from a URL, DOI, or ISBN. For a detailed look at the notes-bibliography alternative, see our guide on how to cite in Chicago notes-bibliography style, or for broader context on in-text citation mechanics across styles, see our complete guide to in-text citations.

How the Author-Date System Works

Each time you paraphrase, summarize, or quote from a source, you include a parenthetical citation in the text. The citation contains the author's last name, the year of publication, and - when citing a specific passage - a page number. At the end of the paper, a reference list provides the full publication details for every source cited.

The Chicago Manual of Style, 18th edition, covers the author-date system in Chapter 15. The general pattern for a parenthetical citation is:

(Author Year, page number)

For example:

Recent studies have challenged the assumption that bilingualism always confers a cognitive advantage (Sanchez 2023, 114).

The corresponding reference list entry would supply the complete bibliographic information for the Sanchez 2023 source.

Parenthetical vs. Narrative Citations

Like APA, Chicago author-date supports two forms of in-text citation:

• Parenthetical: The entire citation appears inside parentheses at the end of the sentence or clause: (Sanchez 2023, 114).
• Narrative: The author's name is woven into the sentence, and only the year (and optional page number) appears in parentheses: Sanchez (2023, 114) found that the cognitive advantage was smaller than previously reported.

Use narrative citations when you want to emphasize the researcher. Use parenthetical citations when the focus should remain on the information itself.

In-Text Citation Rules

One Author

Parenthetical:

The experiment replicated the original findings with a larger sample (Okafor 2024, 87).

Narrative:

Okafor (2024, 87) replicated the original findings with a larger sample.

Two Authors

List both authors separated by "and":

Parenthetical:

Rates of adoption exceeded initial projections (Rivera and Chang 2022, 45).

Narrative:

Rivera and Chang (2022, 45) found that adoption rates exceeded initial projections.

Chicago author-date always uses "and" in text, never an ampersand. This differs from APA, which uses an ampersand inside parentheses.

Three or More Authors

Use the first author's last name followed by "et al." in-text. The reference list should include all authors up to ten; for eleven or more, list the first seven followed by "et al." (Section 15.27).

Parenthetical:

The correlation was statistically significant across all subgroups (Park et al. 2023, 302).

Narrative:

Park et al. (2023, 302) reported a statistically significant correlation across all subgroups.

No Author

When no author is identified, use the title (shortened if necessary) in place of the author name. Italicize book and report titles; put article titles in quotation marks.

Parenthetical:

Global emissions increased by 1.2% over the previous year (Global Climate Report 2024, 8).

Narrative:

According to the Global Climate Report (2024, 8), global emissions increased by 1.2% over the previous year.

No Date

When no publication date is available, use "n.d." (no date) in place of the year:

The manuscript describes rituals that predate the colonial period (Alvarez n.d., 34).

Multiple Works in a Single Citation

Separate multiple sources with semicolons, listed alphabetically or chronologically for the same author:

Several studies support this interpretation (Okafor 2024; Park et al. 2023; Rivera and Chang 2022).

Multiple Works by the Same Author in the Same Year

Distinguish works by appending lowercase letters to the year, in the order the works appear in the reference list:

The findings were consistent across both experiments (Sanchez 2023a, 2023b).

The letters are assigned alphabetically based on the title of each work. The reference list entries must also include the letter after the year.

Page Numbers and Locators

Include a page number whenever you reference a specific passage. Chicago author-date separates the year and page number with a comma:

(Rivera and Chang 2022, 45)

For electronic sources without fixed page numbers, you may use paragraph numbers, section headings, or chapter numbers as locators:

(Torres 2024, chap. 3)

(Lin 2025, under "Results")

Worked Examples

Below are worked examples for five common source types. Each example includes the in-text citation and the corresponding reference list entry.

Book (Single Author)

In-text citation:

Human decision-making relies on predictable heuristics rather than rational calculation (Kahneman 2011, 25).

Reference list entry:

Kahneman, Daniel. 2011. Thinking, Fast and Slow. New York: Farrar, Straus and Giroux.

Note that the author's name is inverted, the year follows immediately, and titles use headline-style capitalization (title case) - unlike APA, which uses sentence case.

Journal Article

In-text citation:

Immigration policy had measurable effects on regional labor markets (Chen and Torres 2024, 220).

Reference list entry:

Chen, Sarah, and Michael Torres. 2024. "Immigration Policy and Labor Markets in the European Union." Journal of Economic History 84, no. 2: 215-240.

Article titles appear in quotation marks with headline-style capitalization. Journal titles are italicized. Include the volume number, issue number, and page range.

Website

In-text citation:

Workplace mental health programs reduce absenteeism by up to 30% (World Health Organization 2025).

Reference list entry:

World Health Organization. 2025. "Mental Health in the Workplace." Last modified March 10, 2025. https://www.who.int/example.

Include the author or organization, year, page title in quotation marks, site name (if different from the author), the date, and URL. If no publication date is available, use "n.d." and include an access date.

Report

In-text citation:

Global carbon dioxide emissions reached a new high in 2024 (United Nations Environment Programme 2024, 12).

Reference list entry:

United Nations Environment Programme. 2024. Emissions Gap Report 2024. Nairobi: UNEP. https://www.unep.org/example.

Reports follow the same format as books. Include a URL or DOI if the report is available online.

Chapter in an Edited Volume

In-text citation:

The relationship between patriotism and cosmopolitanism is more complex than the binary framing suggests (Nussbaum 1996, 10).

Reference list entry:

Nussbaum, Martha. 1996. "Patriotism and Cosmopolitanism." In For Love of Country: Debating the Limits of Patriotism, edited by Joshua Cohen, 3-17. Boston: Beacon Press.

The chapter title is in quotation marks, the book title is italicized and preceded by "In," and the editor is introduced with "edited by."

Building the Reference List

The reference list appears on a new page at the end of the paper with the centered heading "Reference List" or "References." Key formatting rules from Chapter 15:

• Alphabetical order: Entries are sorted alphabetically by the first author's last name. For works with no author, alphabetize by the title (ignoring "A," "An," and "The").
• Hanging indent: The first line of each entry is flush left; subsequent lines are indented 0.5 inches.
• Year placement: The publication year appears immediately after the author's name, followed by a period. This makes it easy for the reader to match the in-text citation (Author Year) to the reference list entry.
• Title capitalization: Use headline-style capitalization (title case) for all titles. This is a key difference from APA, which uses sentence case.
• Multiple works by the same author: Arrange chronologically, earliest first. Replace the author's name with a long dash (3-em dash) after the first entry.
• Multiple works, same author, same year: Add lowercase letters after the year (2023a, 2023b) and alphabetize by title.

Chicago Author-Date vs. APA: Key Differences

Because both Chicago author-date and APA use parenthetical author-year citations, students sometimes confuse the two. The table below highlights the most important differences between Chicago 18th edition author-date and APA 7th edition.

The quickest way to tell the two apart in running text is the comma: Chicago writes (Smith 2024) while APA writes (Smith, 2024). Title capitalization is the other major difference - Chicago uses headline style throughout the reference list, while APA uses sentence case.

Common Mistakes

Adding a comma between author and year. Write (Smith 2024), not (Smith, 2024). The comma before the page number is correct: (Smith 2024, 45). This is the single most common error for students accustomed to APA.

Using sentence case for titles. Chicago uses headline-style capitalization for all reference list titles. Writing Thinking, fast and slow instead of Thinking, Fast and Slow is an APA habit that does not apply here.

Using initials instead of full first names. Chicago reference list entries spell out the author's full first name: "Kahneman, Daniel," not "Kahneman, D." This is another area where APA habits can creep in.

Forgetting the publisher location. Unlike APA 7th edition, which dropped the publisher location requirement, Chicago author-date still includes the place of publication for books: "New York: W. W. Norton," not just "W. W. Norton."

Misapplying et al. in the reference list. In-text citations use "et al." for works with three or more authors, but the reference list should include all authors up to ten. Only abbreviate with "et al." in the reference list when there are eleven or more authors.

Omitting the access date for undated web sources. When a web source has no publication or modification date, include "Accessed [date]" so the reader knows when the content was available. For sources with a clear publication date, the access date is optional.

Quick-Reference Table