Chicago Style Guide (17th Edition)

The Chicago Manual of Style (CMOS) is one of the most widely used and respected citation styles in academic publishing. First published in 1906 by the University of Chicago Press, it has become the standard guide for authors, editors, and publishers in the United States and beyond. The current 17th edition, released in 2017, continues to be the authoritative resource for Chicago style citation format.

Chicago style is favored by many disciplines because of its flexibility and comprehensiveness. Unlike more rigid citation formats, Chicago style offers two distinct documentation systems that cater to different academic needs. This makes it particularly valuable for researchers working with diverse source materials, from historical primary documents to contemporary scientific studies.

The primary users of Chicago style include scholars in history, literature, philosophy, and the humanities, though it also appears in some social sciences and physical sciences. Many university presses, academic journals, and trade publishers require Chicago format for manuscript submissions. Book publishers frequently use Chicago style as their house style, making it essential knowledge for aspiring authors and editors.

What sets Chicago style apart is its emphasis on source documentation through footnotes or endnotes, allowing for extensive commentary without interrupting the flow of the main text. This approach is particularly valuable in historical writing, where authors often need to provide context, acknowledge sources, and engage with secondary literature—all while maintaining readability for their audience.

The Chicago Manual of Style offers two distinct citation systems, each designed for different academic purposes and disciplines. Understanding which system to use is the first step in mastering Chicago style citation format.

Notes and Bibliography (NB) System

The Notes and Bibliography system is the more traditional of the two and is preferred in the humanities—especially history, literature, and the arts. This system uses superscript numbers in the text that correspond to footnotes (at the bottom of the page) or endnotes (at the end of the paper or chapter). These notes provide complete citation information the first time a source is referenced.

A bibliography at the end of the document lists all sources alphabetically, providing full publication details. The bibliography entry format differs slightly from the footnote format, so it's important to follow the specific rules for each. The Notes and Bibliography system allows authors to include substantive commentary in their notes, making it ideal for disciplines where engagement with sources and interpretation are central.

Author-Date (AD) System

The Author-Date system is commonly used in the physical, natural, and social sciences, including disciplines like economics, political science, and sociology. Instead of footnotes or endnotes, this system uses brief parenthetical citations within the text itself, typically including the author's last name, publication year, and page number.

A reference list at the end of the paper provides complete publication information for all sources cited. This system is more concise and better suited to sciences where the focus is on recent research and where extensive commentary in notes is less common. The Author-Date format shares similarities with APA style but maintains Chicago's distinctive approach to source documentation.

The Notes and Bibliography system is the most distinctive feature of Chicago style citation format. Mastering the differences between footnote and bibliography entries is essential for proper documentation.

Book Citations

Books are among the most commonly cited sources in academic writing. Chicago style has specific formatting rules for book citations in both footnotes and the bibliography.

Note the key differences: in the bibliography, the author's last name comes first, and periods replace most parentheses. The publication city appears before the publisher, separated by a colon.

For books with three or more authors, use "et al." in footnotes but list all authors in the bibliography.

Journal Article Citations

Scholarly journal articles require specific information including volume, issue, and page numbers. Chicago format follows a consistent pattern for journal citations.

Note that the bibliography includes the full page range of the article, while the footnote typically cites only the specific page referenced. The volume number is not followed by "vol." and the issue number appears after "no."

Website and Online Source Citations

Citing online sources requires including the URL and, when available, access dates. Chicago style citation format for web sources emphasizes clarity and permanence.

For online sources that may change, include an access date: "accessed August 1, 2023." Use "last modified" when a date is provided, or "published" for formal publications.

Footnote Formatting Rules

• Use superscript numbers in the text, placed after punctuation (except dashes)
• Footnote numbers should begin at 1 and continue consecutively
• Indent the first line of each footnote (use a hanging indent in word processors)
• Use the author's full name in the order First Last
• Titles of books and journals are italicized; titles of articles and chapters are in quotation marks
• Publication information appears in parentheses: (City: Publisher, Year)
• Specific page numbers follow the publication information

Bibliography Formatting Rules

• Start each entry with the author's last name: Last, First
• Alphabetize entries by the authors' last names (or by title if no author)
• Use a hanging indent (second and subsequent lines indented)
• Separate elements with periods instead of parentheses where appropriate
• Include the full page range for articles and chapters
• Single-space within entries, double-space between entries
• For multiple works by the same author, use a 3-em dash (―) instead of the author's name after the first entry

Subsequent Footnote Citations

After citing a source fully in the first footnote, use shortened citations for subsequent references.

Ibid. (short for the Latin ibidem, meaning "in the same place") is used for immediately consecutive citations. If you cite the same source again later (but not immediately after), use the shortened form.

The Author-Date system is favored in sciences and social sciences for its concise in-text citations. Instead of footnotes, sources are cited parenthetically within the text itself.

In-Text Citation Format

Basic in-text citations include the author's last name, publication year, and page number when specific information is referenced.

For two authors: (Smith and Jones 2019, 23). For three or more authors: (Smith et al. 2018, 67).

Reference List Entry - Books

Note that the year follows the author's name immediately, unlike the Notes and Bibliography format where it appears later in the entry.

Reference List Entry - Journal Articles

The year appears after the author's name, and the volume number is not preceded by "vol." The issue number immediately follows the volume in parentheses, followed by a colon and the page range.

Reference List Formatting Rules

• Alphabetize by authors' last names
• Include the publication year after the author's name
• Use a hanging indent for each entry
• Italicize book and journal titles
• Use quotation marks for article and chapter titles
• Capitalize titles using headline style (major words capitalized)
• List multiple works by the same author chronologically, earliest first

Chicago Manual of Style provides guidelines for five levels of headings to create clear hierarchies in academic and professional documents. Proper heading structure helps readers navigate complex texts and understand relationships between ideas.

Headline-Style Capitalization

Chicago style uses headline-style capitalization for most headings. Capitalize the first and last words and all major words (nouns, pronouns, verbs, adjectives, adverbs). Lowercase articles, coordinating conjunctions, and prepositions unless they are the first or last word of the heading or the first word after a colon.

General Heading Guidelines

• Use no more than three levels of headings in most documents
• Leave a blank line before and after each heading (except run-in)
• Number headings only if required by your specific field or publisher
• Keep headings brief and descriptive
• Aave headings stand alone (no "Introduction" as a heading)
• Use parallel structure for headings at the same level

Even experienced writers can make mistakes with Chicago style citation format. Being aware of these common errors will help you avoid them in your own work.

• Confusing the two systems: Mixing Author-Date in-text citations with footnotes, or vice versa. Choose one system and apply it consistently throughout your document.
• Incorrect footnote placement: Superscript numbers should appear after punctuation (except dashes) and quotation marks. Example: "end of the quote."¹ Not: "end of the quote¹."
• Wrong author name format: Footnotes use First Last, while bibliography entries use Last, First. Don't mix these up.
• Missing page numbers: Footnotes require specific page numbers for the referenced information. Bibliography entries need full page ranges for articles and chapters.
• Improper use of Ibid.: Ibid. is only used when citing the same source immediately after the previous citation. If you've cited any other source in between, use a shortened footnote instead.
• Inconsistent punctuation: Chicago style has specific rules for periods, commas, and parentheses in citations. Pay attention to these details.
• Forgetting the bibliography: Even with complete footnotes, you still need a bibliography listing all sources at the end of your paper.
• Wrong capitalization in titles: Use headline-style for most titles, but sentence-style for Level 4 and 5 headings.