Chicago Style of Reference: Notes- Bibliography & Author-Date Style

By Christopher Smith Jun 30, 2025

When you start writing papers in college, "Chicago style" is a name you will hear a lot. It’s one of the most respected and widely used citation styles, but it can also be one of the most confusing. Why? Because there isn’t just one Chicago style—there are two!

The Chicago Manual of Style gives us two different systems for citing sources: Notes-Bibliography and Author-Date.

Think of them like two different tools for the same basic job of giving credit. The Notes-Bibliography style is like a detailed, guided tour, perfect for subjects where you need to discuss your sources. The Author-Date style is like a quick and efficient labeling system, perfect for the sciences.

Which one should you use? Don't worry, this guide will explain everything. We’ll break down both systems with simple explanations and clear examples so you can use Chicago style with confidence.

Which Chicago System Should I Use?

This is the most important question to ask first. The system you use depends on the subject you are writing for.

1. The Notes-Bibliography (NB) System

What it is: This system uses numbered footnotes (notes at the bottom of the page) or endnotes (notes at the end of the paper) to cite sources. It also includes a Bibliography at the end.
Who uses it? It is most popular in the humanities—subjects like History, Literature, Art History, and Philosophy.
Why? The footnote system allows writers to add extra comments and discussions about their sources without cluttering the main text.

2. The Author-Date System

What it is: This system uses brief parenthetical citations right inside the text. They look like this: (Author Last Name Year). It also includes a Reference List at the end.
Who uses it? It is most popular in the social sciences and sciences—subjects like Sociology, Anthropology, Political Science, and sometimes Physics or Biology.
Why? It's a clean and efficient way to show readers who you are citing without making them look away from the text.

The Golden Rule: Always ask your professor or check your assignment guidelines to see which system they want you to use! If they don't specify, choose the one that is most common for your subject.

Part 1: A Deep Dive into the Notes-Bibliography (NB) Style

This is the system with the little numbers and the notes at the bottom of the page. It has two parts: the footnotes and the bibliography.

How to Create Footnotes in NB Style

When you write something that comes from a source, you put a small superscript number at the end of the sentence, after the punctuation.¹ Your word processor (like Word or Google Docs) will automatically create a matching number at the bottom of the page where you can type your citation.

Citing a Source for the FIRST Time

The first time you cite a source, you must give the full details in the footnote.

Footnote for a Book:
- Template: ¹Author's First Name Last Name, Title of Book (Place of Publication: Publisher, Year), Page Number.
- Real Example: ¹John Lewis Gaddis, The Cold War: A New History (New York: Penguin Press, 2005), 45.
Footnote for a Journal Article:
- Template: ¹Author's First Name Last Name, "Title of Article," Name of Journal Volume, no. Issue (Year): Page Number.
- Real Example: ¹Edward Said, "Representing the Colonized: Anthropology's Interlocutors," Critical Inquiry 15, no. 2 (1989): 210.

Citing a Source After the First Time (Shortened Notes)

Once you have given the full citation in one footnote, you can use a much shorter version for every other time you cite that same source.

Template: ²Author's Last Name, Shortened Title, Page Number.
Real Example: ²Gaddis, The Cold War, 52.

How to Create the Bibliography in NB Style

The Bibliography is a separate page at the end of your paper. It is an alphabetized list of every source you used. The formatting is slightly different from the footnotes.

Bibliography Entry for a Book:
- Template: Author's Last Name, First Name. Title of Book. Place of Publication: Publisher, Year.
- Real Example: Gaddis, John Lewis. The Cold War: A New History. New York: Penguin Press, 2005.
Bibliography Entry for a Journal Article:
- Template: Author's Last Name, First Name. "Title of Article." Name of Journal Volume, no. Issue (Year): Full Page Range of Article.
- Real Example: Said, Edward. "Representing the Colonized: Anthropology's Interlocutors." Critical Inquiry 15, no. 2 (1989): 205–25.

Spot the Difference: Notice how in the bibliography, the author's last name comes first, and the punctuation is different from the footnote. The bibliography entry for a journal article also lists the full page range of the article, not just the one you cited.

Part 2: A Deep Dive into the Author-Date Style

This system is cleaner and more direct. It has two parts: the in-text citations and the reference list.

How to Create In-Text Citations in Author-Date Style

You place the citation right inside the text in parentheses.

The Basic Format: (Last Name Year, Page Number)

When you paraphrase or summarize an idea:
- Example: Social capital is a key resource for community development (Putnam 2000).
When you use a direct quote: You MUST include a page number.
- Example: He found that "civic engagement has declined over the last generation" (Putnam 2000, 26).
When you mention the author’s name in your text: The year and page number go in parentheses right after the name.
- Example: According to Putnam (2000, 26), "civic engagement has declined."

How to Create the Reference List in Author-Date Style

The Reference List is a separate page at the end of your paper, alphabetized by the author's last name. It looks very similar to the bibliography in the NB system, with one major difference: the year of publication comes right after the author's name.

Reference List Entry for a Book:
- Template: Last Name, First Name. Year. Title of Book. Place of Publication: Publisher.
- Real Example: Putnam, Robert D. 2000. Bowling Alone: The Collapse and Revival of American Community. New York: Simon & Schuster.
Reference List Entry for a Journal Article:
- Template: Last Name, First Name. Year. "Title of Article." Name of Journal Volume (Issue): Page Range.
- Real Example: Lareau, Annette. 2002. "Invisible Inequality: Social Class and Childrearing in Black Families and White Families." American Sociological Review 67 (5): 747–76.

Spot the Difference: Look closely at the placement of the year. In the Author-Date system, the year comes right after the author's name, making it easy for the reader to connect the reference list entry to the in-text citation they just saw.

Final Tips for Chicago Success

Know Your System: The biggest mistake students make is mixing the two systems. Decide which one you are using and stick to it!
Capitalization: Chicago style uses "headline case" for titles, where you capitalize the main words.
Be a Perfectionist: Getting the small details right, like commas and periods, shows you are a careful scholar. Remember, why citation errors lower your grade and how to avoid them is an important lesson.

You've Got the Tools!

Don’t be intimidated by the big Chicago Manual of Style. Think of its two systems as different tools for different jobs. The Notes-Bibliography system is perfect for detailed discussions in the humanities, while the Author-Date system is a clean and efficient tool for the sciences.

Ask your professor which tool to use, follow the templates in this guide, and you'll be able to present your work with the confidence and professionalism that Chicago style is known for.