Chicago Style Citation Guide: Notes-Bibliography & Author-Date (2026)

Chicago style is one of the most widely used citation systems in academic publishing, and it is unique in offering two distinct documentation methods under one umbrella. Whether you are writing a history thesis that demands detailed footnotes or a social science paper that uses parenthetical references, Chicago style has a system for you.

This guide covers both the Notes-Bibliography (NB) system and the Author-Date (AD) system as defined in the 17th edition of The Chicago Manual of Style (CMOS). We include formatting rules and examples for the most common source types you will encounter in academic writing.

Two Systems, One Manual

The Chicago Manual of Style provides two complete citation systems. Choosing the right one depends on your discipline and your instructor's or publisher's requirements.

Notes-Bibliography (NB)

The Notes-Bibliography system is the traditional Chicago format, preferred in the humanities: history, literature, philosophy, religion, and the arts.

How it works:

1. A superscript number appears in the text at the point of citation.
2. The number corresponds to a footnote (bottom of the page) or endnote (end of the chapter or document) that provides the source details.
3. A bibliography at the end of the document lists all sources in alphabetical order.

Author-Date (AD)

The Author-Date system is used primarily in the sciences and social sciences: biology, sociology, psychology, economics, and related fields.

How it works:

1. A parenthetical citation appears in the text, typically formatted as (Author Year, page).
2. A reference list at the end of the document provides full publication details for every source cited, listed alphabetically by author.

Notes-Bibliography System: Complete Guide

Footnote and Endnote Format

The first time you cite a source, the footnote includes full publication details. Subsequent citations of the same source use a shortened form.

First reference (full note)

The full note includes the author's full name (first name first), the title, and complete publication information. The exact format varies by source type, as shown in the examples below.

Subsequent references (short note)

After the first full citation, use a shortened form:

2. Morrison, Song of Solomon, 45.

This includes only the author's last name, a shortened title (italicized for books, in quotation marks for articles), and the page number.

Ibid.

When citing the same source as the immediately preceding footnote, you may use "Ibid." (capitalized at the start of a note, followed by a period):

3. Ibid., 52.

If the page number is the same as the preceding note, use "Ibid." alone without a page number. Note that some style guides and instructors discourage the use of Ibid. -- check your specific requirements.

Bibliography Format

Bibliography entries differ from footnotes in three key ways:

1. The first author's name is inverted (Last name, First name).
2. The entry uses periods instead of commas to separate major elements.
3. Page ranges are included for articles and chapters (but not for books cited as a whole).

Entries are listed alphabetically by the first author's last name. Single-author entries come before multi-author entries beginning with the same name.

Notes-Bibliography Examples by Source Type

Book (single author)

Footnote (first reference):

1. Michelle Alexander, The New Jim Crow: Mass Incarceration in the Age of Colorblindness (New York: New Press, 2010), 31.

Footnote (short form):

5. Alexander, New Jim Crow, 31.

Bibliography:

Alexander, Michelle. The New Jim Crow: Mass Incarceration in the Age of Colorblindness. New York: New Press, 2010.

Book (two or more authors)

Footnote:

2. Steven Levitsky and Daniel Ziblatt, How Democracies Die (New York: Crown, 2018), 102.

For books with three or more authors, list all authors in the footnote the first time. In subsequent references, use the first author's last name followed by "et al."

Bibliography:

Levitsky, Steven, and Daniel Ziblatt. How Democracies Die. New York: Crown, 2018.

For four or more authors, the bibliography entry may list all authors or use the first author followed by "et al." -- follow your instructor's preference.

Edited book

Footnote:

3. James Chandler, ed., The Cambridge History of English Romantic Literature (Cambridge: Cambridge University Press, 2009), 215.

Bibliography:

Chandler, James, ed. The Cambridge History of English Romantic Literature. Cambridge: Cambridge University Press, 2009.

Chapter in an edited book

Footnote:

4. Anne Hartigan, "The Persistence of Memory in Irish Literature," in The Cambridge Companion to Modern Irish Culture, ed. Joe Cleary and Claire Connolly (Cambridge: Cambridge University Press, 2005), 45--60.

Bibliography:

Hartigan, Anne. "The Persistence of Memory in Irish Literature." In The Cambridge Companion to Modern Irish Culture, edited by Joe Cleary and Claire Connolly, 45--60. Cambridge: Cambridge University Press, 2005.

Journal article

Footnote:

5. Sarah Richardson, "Race and IQ in the Postgenomic Age," American Journal of Physical Anthropology 175, no. 2 (2021): 410--24.

Bibliography:

Richardson, Sarah. "Race and IQ in the Postgenomic Age." American Journal of Physical Anthropology 175, no. 2 (2021): 410--24.

If the article has a DOI, include it at the end:

Richardson, Sarah. "Race and IQ in the Postgenomic Age." American Journal of Physical Anthropology 175, no. 2 (2021): 410--24. https://doi.org/10.1002/ajpa.24150.

Website or webpage

Footnote:

6. World Health Organization, "Antimicrobial Resistance," last modified November 21, 2023, https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance.

Bibliography:

World Health Organization. "Antimicrobial Resistance." Last modified November 21, 2023. https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance.

If no author is listed, begin with the organization or site name. Include the URL and an access date if no publication or modification date is available.

Newspaper or magazine article

Footnote:

7. Jennifer Schuessler, "The Surprising History of the Word 'Woke,'" New York Times, October 14, 2023.

Bibliography:

Schuessler, Jennifer. "The Surprising History of the Word 'Woke.'" New York Times, October 14, 2023.

Newspaper articles may be omitted from the bibliography if they are cited fully in the notes. Check your instructor's preference.

Thesis or dissertation

Footnote:

8. Maria Chen, "Neural Correlates of Decision-Making under Uncertainty" (PhD diss., Stanford University, 2022), 87.

Bibliography:

Chen, Maria. "Neural Correlates of Decision-Making under Uncertainty." PhD diss., Stanford University, 2022.

Conference paper

Footnote:

9. David Park and Elena Sokolova, "Transformer Architectures for Low-Resource Languages" (paper presented at the Annual Meeting of the Association for Computational Linguistics, Toronto, Canada, July 2023), 12.

Bibliography:

Park, David, and Elena Sokolova. "Transformer Architectures for Low-Resource Languages." Paper presented at the Annual Meeting of the Association for Computational Linguistics, Toronto, Canada, July 2023.

Author-Date System: Complete Guide

In-Text Citations

Author-Date in-text citations are parenthetical references placed within the sentence, typically before the period. The basic format is:

(Author Year, page)

Examples:

• One author: (Alexander 2010, 31)
• Two authors: (Levitsky and Ziblatt 2018, 102)
• Three or more authors: (Park et al. 2023, 12)
• Multiple works by the same author in the same year: (Smith 2020a, 45) and (Smith 2020b, 112)
• Multiple works in one citation: (Alexander 2010, 31; Levitsky and Ziblatt 2018, 102)

If the author's name appears in the sentence, only the year and page number go in parentheses:

Alexander (2010, 31) argues that the criminal justice system functions as a racial caste system.

Reference List Format

Reference list entries in the Author-Date system place the year immediately after the author's name. Entries are alphabetized by the first author's last name.

Author-Date Examples by Source Type

Book (single author)

Alexander, Michelle. 2010. The New Jim Crow: Mass Incarceration in the Age of Colorblindness. New York: New Press.

Book (two or more authors)

Levitsky, Steven, and Daniel Ziblatt. 2018. How Democracies Die. New York: Crown.

Edited book

Chandler, James, ed. 2009. The Cambridge History of English Romantic Literature. Cambridge: Cambridge University Press.

Chapter in an edited book

Hartigan, Anne. 2005. "The Persistence of Memory in Irish Literature." In The Cambridge Companion to Modern Irish Culture, edited by Joe Cleary and Claire Connolly, 45--60. Cambridge: Cambridge University Press.

Journal article

Richardson, Sarah. 2021. "Race and IQ in the Postgenomic Age." American Journal of Physical Anthropology 175 (2): 410--24. https://doi.org/10.1002/ajpa.24150.

Note the difference from NB format: the year follows the author, and the volume/issue format uses parentheses around the issue number rather than "no."

Website or webpage

World Health Organization. 2023. "Antimicrobial Resistance." Last modified November 21, 2023. https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance.

Newspaper or magazine article

Schuessler, Jennifer. 2023. "The Surprising History of the Word 'Woke.'" New York Times, October 14, 2023.

Thesis or dissertation

Chen, Maria. 2022. "Neural Correlates of Decision-Making under Uncertainty." PhD diss., Stanford University.

Conference paper

Park, David, and Elena Sokolova. 2023. "Transformer Architectures for Low-Resource Languages." Paper presented at the Annual Meeting of the Association for Computational Linguistics, Toronto, Canada, July 2023.

Key Differences Between NB and AD at a Glance

Formatting Your Chicago Paper

Beyond citations, CMOS provides guidance on paper formatting. The most common requirements include:

General formatting

• Font: 12-point Times New Roman or equivalent serif font.
• Margins: 1 inch on all sides.
• Spacing: Double-spaced body text. Footnotes and bibliography entries may be single-spaced with a blank line between entries (check your instructor's preference).
• Page numbers: Placed in the header, top right, beginning with the first page of text.

Title page

Chicago does not require a title page for shorter papers, but many instructors expect one. If included, center the title one-third down from the top, followed by the author's name and course information.

Block quotations

Quotations of five or more lines should be set off as a block quotation: indented half an inch from the left margin, single-spaced (or the same spacing as the rest of the text, depending on your instructor), and without quotation marks.

Headings

CMOS does not prescribe a rigid heading hierarchy, but a common approach uses:

• Level 1: Centered, bold
• Level 2: Centered, italic
• Level 3: Flush left, bold
• Level 4: Flush left, italic

Common Chicago Style Mistakes

1. Confusing the two systems

The most common mistake is mixing NB and AD elements in the same paper. If you are using footnotes, do not include parenthetical author-date citations, and vice versa. Pick one system and use it consistently.

2. Omitting the bibliography

Some students assume that footnotes alone are sufficient. The bibliography is a required component of the NB system unless your instructor explicitly states otherwise.

3. Incorrect shortened notes

The shortened note form requires a shortened title, not just the author's last name. "Morrison, 45" is incorrect. "Morrison, Song of Solomon, 45" is correct.

4. Missing access dates for URLs

For online sources without a publication or modification date, Chicago requires an access date: "Accessed March 11, 2026." If the source has a clear publication date, the access date is optional but recommended for content that may change.

5. Wrong punctuation in bibliography entries

Bibliography entries use periods between major elements (author, title, publication information). Footnotes use commas. Swapping these punctuation marks is a frequent error.

When to Use Chicago Style

Chicago style is required or preferred by many institutions and publishers:

• History departments at most universities require NB format.
• University presses (Chicago, Oxford, Harvard, etc.) generally follow CMOS.
• Humanities journals in literature, philosophy, and religious studies typically use NB.
• Some social science journals accept or prefer Author-Date.
• Turabian-based coursework at many colleges follows Chicago style with minor modifications.

If your instructor simply says "use Chicago," confirm which system (NB or AD) they expect. Submitting a paper in the wrong system is a common and easily avoidable mistake.

Chicago Style and Digital Sources

The 17th edition of CMOS expanded its coverage of digital sources significantly. A few key points:

DOIs and URLs

Always include a DOI when one is available. DOIs are preferred over URLs because they are persistent identifiers. Format DOIs as full URLs: https://doi.org/10.xxxx/xxxxx.

When no DOI is available, include the URL. If the URL is excessively long, you may use the URL of the site's home page or main page for the work, or a shortened URL.

Social media

Chicago provides formats for citing social media posts. The general pattern includes the author, text of the post (up to 160 characters), the platform name, the date, and the URL.

E-books

For e-books, include the format or platform (Kindle, Apple Books, PDF) after the publisher information if the format affects pagination. If the e-book has stable page numbers matching the print edition, cite page numbers normally.

Free Tools for Chicago Citations

Formatting Chicago citations manually is time-consuming, particularly for the NB system where you need both full and short note forms plus the bibliography entry for every source. Several tools can help:

• CiteDash -- AI-powered citation generation with automatic formatting in both Chicago systems. Validates sources against academic databases.
• ZoteroBib -- Free bibliography generator from the Zotero team.
• Your university library -- Many academic libraries provide access to citation management tools and formatting guides.

The key advantage of using a dedicated tool is consistency. Chicago style has dozens of rules that vary by source type, and even experienced researchers make formatting errors when working manually.

Final Thoughts

Chicago style is demanding but logical. Once you understand the core distinction between Notes-Bibliography and Author-Date, and once you learn the patterns for each source type, the system becomes predictable. The key is consistency: choose one system, apply it uniformly, and verify every citation before submission.

For detailed guidance on edge cases not covered here, consult the Chicago Manual of Style Online (available through most university libraries) or Turabian's A Manual for Writers for student-specific formatting guidance.