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The Chicago Manual of Style, explained

The Chicago Manual of Style is an American English style guide published by the University of Chicago Press. The Manual’s guidelines for publishing, style and usage, and citations and indexes—known as “Chicago style” rules and recommendations—are among the most widely used in the United States, especially in academic and book publishing.

What is The Chicago Manual of Style?

The Chicago Manual of Style is an American English style and usage guide published continuously by the University of Chicago Press since 1906. Today, it is used widely in many academic disciplines and is considered the standard for US style in book publishing.

The Chicago Manual of Style has become a staple reference for writers and editors, in part because it was one of the first style guides to be published in book form, and the only one from an academic press in North America. (Other style guides are published by professional associations.) Eventually, the Manual became a canonical work synonymous with its home institution, akin to the Oxford English Dictionary.

The Manual is now in its 17th edition, published in 2017. Sometimes referred to by its acronym, CMOS (pronounced like “sea moss”), The Chicago Manual of Style is available both in print and online, for an annual subscription fee. A free Chicago style Q&A and other resources are also available to the public on the CMOS website.

Grammar enthusiasts celebrate “Chicago style” rules, such as whether to put the title of a book in italics (Chicago style says yes, whereas AP style recommends quotation marks), or whether to use a serial comma—also known as an “Oxford” comma (Chicago style: yes; AP style: no). However, the editors at the University of Chicago Press acknowledge that rules are often context-dependent, and sometimes need to be broken. The Manual is thus also respected for its flexibility.

What is the history of The Chicago Manual of Style?

Opening in 1891, the University of Chicago Press was one of the original divisions of the University of Chicago (founded in 1890). The staff at the Press soon decided that maintaining a consistent, professional style would be essential to streamlining the Press’s publishing across many disciplines, and drew up an initial style sheet that was circulated to the university community.

The first iteration of the Manual as we know it today was published in 1906 as Manual of Style: Being a Compilation of the Typographical Rules in Force at the University of Chicago Press, to Which Are Appended Specimens of Type in Use.

The Manual has been revised numerous times, including a major revision—the 12th edition in 1969—that definitively established the Manual as an industry leader on style matters. The first edition to incorporate “Chicago” in the title was the 13th edition, published in 1982; previous titles had been variations on A Manual of Style. The change reflected the way readers typically referred to the manual.

Over the years, each edition has sought to address contemporary questions from readers that have arisen via the continued evolution of language and technology. For example, the proliferation of computers—including digital publishing techniques facilitated by the internet and social media—have created a host of new style-related questions, many of which are addressed in recent editions.

Historical content adapted from The Chicago Manual of Style Online.

What is Turabian style?

The term “Turabian” or “Turabian style” refers to the style guidelines that serve as a standard reference for college and graduate students writing research papers, providing an introduction to Chicago-style formatting and citation.

The guidelines were first set forth in 1937 by Kate L. Turabian—then the University of Chicago’s graduate school dissertation secretary—who wrote the pamphlet that became A Manual for Writers of Research Papers, Theses, and Dissertations. Now in its ninth edition, with multiple contributing writers and editors, Turabian (as it is usually known) continues to emphasize the value of strong research questions, evidence-based arguments, logical structure, and source citation.

The Turabian style guide is published by the University of Chicago Press and closely follows The Chicago Manual of Style, such that the term “Chicago/Turabian” is also used in some instances. The primary differences are the scope of the Turabian guide, which is narrower than that of CMOS, and its target audience of students. More information about the Turabian style guide and its history is available on The Chicago Manual of Style’s website.

What makes something definitively Chicago style?

When people talk about “Chicago style” rules, they are most often referring either to punctuation or source citations. In the case of punctuation, Chicago is the standard for US style in book publishing, whereas Oxford style is generally associated with British style. Some examples of a few notable differences are below:

  • Chicago prefers double quotation marks (“like this”); Oxford prefers single (‘like this’).
  • In Chicago style, periods and commas go inside closing quotation marks, “like this,” whereas Oxford puts them after, ‘like this’, though there are exceptions (and exceptions are generally made in British style for fiction and journalism).
  • Chicago uses em dashes with no space before or after—like this. Usage at Oxford varies, but in British style many publishers prefer spaced en dashes – like this.
  • Oxford style is usually associated with the “Oxford comma”—the comma before the conjunction in a series of three or more (like the one before “and” in “apples, oranges, and pears”). But this comma has also always been Chicago style. CMOS refers to it as a “serial comma.”
  • On spelling, Chicago prefers the spellings at Merriam-Webster.com; Oxford follows Oxford’s dictionaries, starting with the Oxford English Dictionary.

Source citations involve the use of numbered notes and a bibliography, each styled and punctuated in a specific way, or author-date citations. Chicago’s citation style, like many of its other rules, goes back to the first edition and its focus on academic publishing. For more information about Chicago-style citations, read on.

This section was adapted from content contributed by Russell Harper, the editor of The Chicago Manual of Style’s Online Q&A.

What is a Chicago-style citation? Is a quick reference available for Chicago style?

For detailed information about Chicago-style citations and references, visit the CMOS website and Citation Quick Guide. In general, Chicago-style citations use either an author-date format or numbered notes and a bibliography.

Here is an example of an author-date citation, as it would appear in the text of an essay citing a book:

The primary cheeses used in Chicago-style pizza are mozzarella, Parmesan, and Romano (Bruno 1983, 4).

Here is a full citation for the same book, as it would appear at the end in a list of works cited:

Bruno, Pasquale, Jr. The Great Chicago-Style Pizza Cookbook. New York: McGraw-Hill, 1983.

Here is how the same book would appear as a footnote with a corresponding reference:

Sentence from essay: For best results, stick to high-quality tomatoes, and avoid adding tomato paste to your Chicago-style pizza sauce.¹

Reference at the bottom of the page or end of the text: 1. Pasquale Bruno Jr., The Great Chicago-Style Pizza Cookbook (New York: McGraw-Hill, 1983), 3.

What is the difference between Chicago style, AP style, MLA style, and APA style? In what contexts is Chicago style used most often?

Many English style and usage guides exist, and many organizations have their own in-house guides. Some guides are specific to particular fields like law, whereas others have more general applications.

There are many guides in publishing, media, and academia, but four predominate. These are the Associated Press Stylebook (AP style), The Chicago Manual of Style (Chicago style), the Modern Language Association’s MLA Handbook (MLA style), and the Publication Manual of the American Psychological Association (APA style). AP style is the standard in journalism, while MLA style is popular in classroom instruction and in some academic disciplines. APA style is often used in the social sciences and related academic fields.

Chicago style is comprehensive, and can address most questions relevant to writing, editing, and publishing in any discipline. Intended originally as a guide for publishers of academic books and journals, it is especially popular in the humanities and social sciences. Chicago style is also used widely by students and by publishers of novels and trade books.

Here is an example of the differences between Chicago style and AP style on common questions, such as styling titles in italics or quotations marks, the use of serial or “Oxford” commas, and possessive nouns ending in the letter “s”:

Chicago style: After Harry Styles’s tour in support of his album Fine Line stopped at the United Center, the pop star made sure to pick up some Chicago-style pizza, hot dogs, and popcorn.

AP style: After Harry Styles’ tour in support of his album “Fine Line” stopped at the United Center, the pop star made sure to pick up some Chicago-style pizza, hot dogs and popcorn.

Though either guide’s recommendations might seem prescriptive, English is a fraught language, with many potential gray areas. The editors at the University of Chicago Press (like those at AP) have sought to establish clarity and consistency while at the same time remaining flexible and cognizant of the fact that context may call for individual discretion on style matters.

How did The Chicago Manual of Style become a standard reference?

The Chicago Manual of Style became a standard reference in part because of its early publication date at a time when university press publishing in the United States was just getting off the ground. Today, the University of Chicago Press is considered the largest academic press in the United States. It is also one of the oldest continuously publishing presses, according to the Association of American University Presses, with Johns Hopkins University Press (founded in 1878) being the oldest.

The University of Chicago Press quickly began to establish itself as a leading American university press, publishing the first edition of the Manual in 1906, before some competing presses, like those at Yale University (1908) and Harvard University (1913), had even been established.

In the United Kingdom, however, Oxford University Press began publishing its own style guide, originally titled Rules for Compositors and Readers at the University Press, Oxford, in 1904 (two years before Chicago). Known informally as “Hart’s Rules,” after the original author, Horace Hart, the Oxford style guide continues to be published today, with the most recent edition titled New Oxford Style Manual (2016).

Oxford University Press and other presses such as Cambridge University Press are older than any North American university press. Oxford traces the founding of its press to the 16th century (as does Cambridge). However, both the University of Chicago and the University of Oxford made their style guides available to the public before competitors early in the 20th century, which helped ensure their influence since then.

University of Chicago faculty, students, and staff can access The Chicago Manual of Style Online from the Library home page.

Editor’s Note: UChicago News follows journalistic convention, meaning that most of our coverage is published in AP style. However, an exception has been made for this piece, which is published in Chicago style in keeping with its subject matter.