Chicago style citation uses one of two systems: notes and bibliography, which places numbered footnotes or endnotes throughout your text, or author-date, which uses parenthetical references. Both systems are governed by the Chicago Manual of Style, now in its 18th edition. The system you choose depends on your field of study and, often, your instructor’s preference.
Notes-Bibliography vs. Author-Date
The two Chicago citation systems look very different on the page but share the same underlying rules for how you format author names, titles, and publication details. The difference is in how you point the reader to your sources.
In the notes and bibliography system, you place a superscript number at the end of a sentence where you reference a source. That number corresponds to a footnote at the bottom of the page (or an endnote at the end of the paper) containing the full citation. You also compile all your sources in a bibliography at the end. This system is the older and more flexible of the two, and it handles unusual source types more gracefully. It’s the standard in the humanities: literature, history, philosophy, and the arts.
In the author-date system, you insert a brief parenthetical citation in the text, typically the author’s last name and the year of publication, like (Binder and Kidder 2022, 117). Each parenthetical matches an entry in a reference list at the end of your paper. This system highlights when research was published, which matters more in fields where findings get updated frequently. It’s preferred in the sciences and social sciences.
If your professor or publisher hasn’t specified which system to use, pick the one that matches your discipline. When in doubt for a humanities paper, go with notes and bibliography.
How to Format a Notes-Bibliography Citation
Every time you quote, paraphrase, or reference a source, you insert a superscript number in the text. The first time you cite a source, the corresponding footnote or endnote contains the full citation. After that, you use a shortened form: typically just the author’s last name, a shortened title, and the page number. The 18th edition lets you choose between author-title, author-only, or title-only for these shortened citations.
Your bibliography goes at the end of the paper and lists every source alphabetically by the author’s last name. The key formatting difference between a note and a bibliography entry is the order and punctuation. In a note, the author’s name appears in normal order (first name, last name) and elements are separated by commas. In a bibliography entry, the first author’s name is inverted (last name, first name) and major elements are separated by periods.
Book
The 18th edition made a significant change: you no longer need to include a place of publication when citing books. A note for a book looks like this:
- Note: 1. Amy J. Binder and Jeffrey L. Kidder, The Channels of Student Activism (University of Chicago Press, 2022), 117.
- Bibliography: Binder, Amy J., and Jeffrey L. Kidder. The Channels of Student Activism: How the Left and Right Are Winning (and Losing) in Campus Politics Today. University of Chicago Press, 2022.
Journal Article
Journal articles require the article title in quotation marks, the journal name in italics, the volume number, and a page range. You can now omit the month or season of publication. Include a DOI (a permanent digital link) when one is available.
Chapter in an Edited Book
When citing a single chapter from a book with multiple contributors, list the chapter author first, then the chapter title in quotation marks, followed by “in” and the book title in italics, then “edited by” and the editor’s name. The 18th edition no longer requires the page range for the chapter in your bibliography entry, though you still include the specific page you’re referencing in a footnote.
How to Format an Author-Date Citation
The in-text citation goes inside parentheses, usually at the end of the sentence before the period. Include the author’s last name, the publication year, and a page number when you’re referencing a specific passage.
For a book with two authors, list both names: (Binder and Kidder 2022, 117). For three or more authors, list only the first author followed by “et al.”: (Snyder et al. 2024, 230). In your reference list at the end of the paper, you can include up to six authors. If a source has more than six, list the first three followed by “et al.”
A reference list entry for a book looks like this:
Binder, Amy J., and Jeffrey L. Kidder. 2022. The Channels of Student Activism: How the Left and Right Are Winning (and Losing) in Campus Politics Today. University of Chicago Press.
Notice the year comes right after the author’s name, which is what makes it easy for readers to match the parenthetical citation to the right entry. A reference list entry for a chapter in an edited book follows the same pattern:
Doyle, Kathleen. 2023. “The Queen Mary Psalter.” In The Book by Design: The Remarkable Story of the World’s Greatest Invention, edited by P. M. Marks and Stephen Parkin. University of Chicago Press.
Handling Author Lists
The 18th edition tightened the rules on how many authors you list. In a bibliography or reference list, include up to six authors. If there are more than six, list only the first three followed by “et al.” In footnotes and in-text citations, include up to two authors. If there are more than two, list only the first followed by “et al.”
One other change worth noting: Chicago now prefers that you repeat an author’s full name in your bibliography when they appear in multiple entries. Previous editions used a 3-em dash as a stand-in for repeated names. If you’re following the 18th edition, spell the name out each time.
Citing Websites and Digital Sources
For a website, include the author (if known), the title of the page or article in quotation marks, the name of the website in italics, and a URL. If the content has a publication or revision date, include it. If not, include an access date. The 18th edition now says website names should be italicized when they fall into a category that would normally be italicized, such as a periodical or publication.
For social media posts, include the author’s name (or handle), the text of the post (up to the first 160 characters or so), the platform name, and the date. Treat the post text as a title in quotation marks.
Citing AI-Generated Content
The 18th edition added guidance for citing AI tools like ChatGPT. If you used an AI tool in any part of your writing process, whether to gather information, draft text, edit, synthesize ideas, or manipulate data, you need to cite it. Your citation should include the tool’s name and version (for example, ChatGPT 4), the date you used it, the prompt you entered, and the response you received. Most citation management tools don’t yet have a built-in format for AI sources, so you’ll likely need to create these citations manually.
Before citing AI content, check your instructor’s or publisher’s policy. Some courses and journals restrict or prohibit AI use entirely, which makes the citation question moot.
Paper Formatting Basics
Chicago style has specific requirements for the physical layout of your paper. Set margins at one inch or wider on all sides. Use a readable font like Times New Roman in 12-point size (10-point is the minimum, but 12 is standard). Page numbers start on the first page of body text, placed in the header, using Arabic numerals beginning with 1.
For your title page, center the title about a third of the way down the page. If you have a subtitle, end the title line with a colon and place the subtitle on the next line. Your name, course information, and date go several lines below, also centered. Double-space everything on the title page.
Key Changes in the 18th Edition
If you learned Chicago style from an earlier edition, a few updates in the 18th edition will affect how your citations look. The most practical changes:
- No place of publication needed for books. You can drop the city name entirely.
- Repeat author names in bibliographies. Stop using the 3-em dash for consecutive entries by the same author.
- Up to six authors in bibliographies, three max for longer lists. Previously, up to ten authors were listed.
- Page ranges optional for book chapters. You still need them for journal articles.
- Self-published books should use the phrase “published by the author” (or “pub. by author” in a note) rather than “self-published.” You no longer need to name a distribution platform like Amazon.
- Capitalize prepositions of five or more letters in titles. “A Room with a View” but “Much Ado About Nothing.”
- Capitalize the first word after a colon when it begins a complete sentence.
These changes simplify citation in most cases, particularly the removal of publication locations, which were often hard to track down for newer books. If you’re unsure which edition your course requires, ask your instructor. The differences are small enough that they rarely cause problems, but getting the details right signals careful work.