Chicago is one of the two giants of American academic style. The Chicago Manual of Style runs to over a thousand pages and covers grammar, usage, manuscript preparation, indexing, copyright, and two distinct citation systems. This guide is the orientation to both citation systems: Author-Date for social science writing and Notes-Bibliography for humanities writing.
The canonical reference is the Chicago Manual of Style, 18th Edition, published by the University of Chicago Press in 2024. CMOS keeps a public companion at chicagomanualofstyle.org with a Q&A archive and free articles, and the full Manual is available to subscribers online and in print. This blog post is an orientation. It is not a rulebook and does not replace the Manual when you need a canonical answer.
Where Chicago came from and who uses it
The University of Chicago Press published the first edition of A Manual of Style in 1906 as an in-house style sheet for the press itself. Over more than a century and seventeen subsequent editions, it has become the most comprehensive American style guide in print. CMOS 18 is the current edition.
The Manual carries two parallel citation systems on purpose. The Author-Date system suits scientific and social-scientific writing where author and year are the information a reader most often wants at a glance. The Notes-Bibliography system suits humanities writing where engagement with specific passages and the texture of footnoted commentary matter.
Disciplines that typically use Author-Date include sociology, political science, anthropology, education, business administration, public policy, and many interdisciplinary fields. Disciplines that typically use Notes-Bibliography include history, art history, classics, religious studies, philosophy, musicology, theater studies, and large parts of literary studies that prefer Chicago over MLA.
The mechanics: spelling, punctuation, and usage
These rules are the same in both systems. The mechanics chapters of the Manual do not branch by citation style.
Spelling
American spelling is the default. Where multiple American spellings exist, CMOS uses Merriam-Webster’s Collegiate Dictionary as the tiebreaker. For technical or specialized terms, the appropriate subject dictionary takes priority.
Punctuation
Chicago uses American punctuation. Commas and periods sit inside closing quotation marks regardless of whether they belong to the quoted material. Semicolons and colons sit outside.
CMOS requires the serial comma. The Manual is firm on this: lists of three or more items always carry the comma before the final “and” or “or.” Block quotations are used for prose of approximately 100 words or more (about five lines), set off from the surrounding text by indentation rather than quotation marks.
Numbers
Chicago has two number conventions and lets writers pick which one to use. The general rule, which CMOS recommends for most non-technical writing, spells out whole numbers through one hundred and uses figures from 101 onward. The alternative rule, common in scientific and technical writing, uses figures from 10 onward. Whichever rule you pick, use it consistently across the document.
Capitalization
Chicago uses headline-style capitalization (close to title case) for the titles of books, journals, articles, and chapters, in running text and in the reference list, notes, and bibliography. Both systems follow the same rule, so a title looks the same whichever system you use.
Italics
Book titles, journal titles, newspaper titles, film titles, and the names of long-form works are italic in running text and in the reference list or bibliography. Article titles, chapter titles, and short-form titles use roman type, usually inside quotation marks. The abbreviation et al. is not italicized in Chicago, in line with most American style guides outside the Harvard family.
The two citation systems, at a glance
Both systems link two parts of your document: the citation in the body and the full source information at the end.
- Author-Date: short parenthetical in the running text + an alphabetical reference list at the end. Example shape: (Stein 2019, 47) in the body; Stein, Mara. 2019. Quiet Revisions ... at the end.
- Notes-Bibliography: superscript numeral in the running text + a numbered note (footnote or endnote) + an alphabetical bibliography at the end. Example shape: a small ¹ after the cited sentence; the note carries the full citation; the bibliography lists every cited source.
The sections below cover each system in turn.
Chicago Author-Date
How in-text citations work
An Author-Date citation contains the author surname and the year of publication. A page number is added when you are citing a direct quotation or a specific passage worth pointing the reader to, but is not required for general paraphrase that draws on the source as a whole. No comma sits between author and year.
Parenthetical citations tuck both elements into parentheses at the end of the sentence:
The narrator’s reliability begins to dissolve in the second movement of the novel (Okonkwo 2022, 47).
Narrative citations weave the author surname into the sentence and follow it with the year (and page, when relevant) in parentheses:
Okonkwo (2022, 47) argues that the narrator’s reliability begins to dissolve in the second movement of the novel.
Multiple authors
For two authors, both surnames appear in citations. For three or more authors, only the first surname appears, followed by et al. without italic: (Choi et al. 2021). In the reference list itself, list up to six authors; for more than six, list the first three followed by et al.
Multiple sources together
Several sources supporting the same point appear in one set of parentheses, separated by semicolons: (Choi 2021; Okonkwo 2022; Stein 2019). Chicago leaves the order to you: follow the order of the material, or the relative importance of the sources, and otherwise use alphabetical or chronological order consistently.
In-text examples to internalize
- One author, parenthetical, paraphrase: The setting carries the mood of the chapter (Stein 2019).
- One author, narrative, with page reference: Stein (2019, 122) suggests that the chapter rests on a single image.
- Three or more authors, et al.: The argument turns on one sentence (Choi et al. 2021, 88).
- Multiple sources in one citation: Several readings converge on the point (Choi 2021; Okonkwo 2022; Stein 2019).
The reference list
The reference list sits at the end of the document, starts on a new page, and carries the heading “References.” Entries are alphabetical by first author surname and formatted with a hanging indent.
Each entry follows the four-part skeleton: who, when, what, where. The exact shape depends on the source type. CMOS Author-Date places the year directly after the author (without parentheses) so that alphabetical-by-author-then-by-year sorting is trivial.
Reference list examples
- Book: Stein, Mara. 2019. Quiet Revisions: Editing as a Craft. Bracewell Press.
- Journal article: Okonkwo, Adaeze C. 2022. “Reading between the Citations.” Journal of Humanistic Inquiry 14 (2): 121–44. https://doi.org/10.1234/jhi.2022.047.
- Chapter in an edited book: Choi, Jiwon. 2021. “On Voice.” In The Shape of Scholarly Prose, edited by Mara Stein, 88–112. Bracewell Press.
- Online article: Patel, Riya. 2022. “Form and Feeling in Recent Criticism.” Modern Letters Review 8 (4): 12–34. https://example.org/mlr/12345.
Things to remember about the reference list
- Alphabetical order by first author surname; secondary sort by year for the same author.
- Hanging indent on every entry.
- Headline-style capitalization for book, journal, article, and chapter titles.
- Italic for book and journal titles. Roman type with quotation marks for article and chapter titles.
- Year follows the author directly, without parentheses.
- DOIs as URLs when available, with the https://doi.org/ prefix.
- No place of publication for books. CMOS 18 no longer requires it; the publisher and year are enough.
Chicago Notes-Bibliography
How notes work
Notes-Bibliography is a two-part system. In the running text, the writer adds a superscript number at the end of the sentence (or the relevant clause), and a numbered note carries the citation, either at the foot of the page or grouped at the end of the document. The first time you cite a source, the note carries the full citation. Every subsequent time you cite the same source, the note carries a shortened citation that names the author and a short version of the title.
First full citation
The first time a source is cited, the note carries the author name in normal order (first name first), the title, the publication information, and the specific page or pages being cited. Pieces are separated by commas rather than periods. The note ends with a period.
- Book, first full citation: 1. Mara Stein, Quiet Revisions: Editing as a Craft (Bracewell Press, 2019), 47.
- Journal article, first full citation: 2. Adaeze C. Okonkwo, “Reading between the Citations,” Journal of Humanistic Inquiry 14, no. 2 (2022): 121–44, https://doi.org/10.1234/jhi.2022.047.
- Chapter in an edited book, first full citation: 3. Jiwon Choi, “On Voice,” in The Shape of Scholarly Prose, ed. Mara Stein (Bracewell Press, 2021), 88–112.
- Website article, first full citation: 4. Riya Patel and Mahesh Poudyal, “Form and Feeling in Recent Criticism,” Modern Letters Review, March 14, 2022, https://example.org/mlr/12345.
Shortened citations
Every subsequent citation of the same source uses a shortened form: the author surname, a short version of the title, and the page being cited.
- Book, shortened citation: 5. Stein, Quiet Revisions, 122.
- Journal article, shortened citation: 6. Okonkwo, “Reading between the Citations,” 130.
When two consecutive notes cite the same source and the same passage, recent CMOS recommends a repeated shortened citation rather than ibid. The repeat is more durable when notes get reordered during editing.
Multiple authors in a note
For two authors, both names appear in the notes and the bibliography. For three or more authors, a note gives only the first author name followed by et al. The bibliography lists up to six authors; for more than six, it lists the first three followed by et al. These are the same thresholds used in Chicago Author-Date.
The bibliography
The bibliography starts on a new page after the body of the document with the heading “Bibliography” centered at the top. Entries are alphabetical by first author surname, formatted with a hanging indent. Author names are inverted (surname first) in the bibliography, in contrast with the notes, where the first author appears in natural order.
Each bibliography entry carries the same core elements, who, what, where, and when, with periods between the major divisions and the year near the end. The bibliography entry contains the same information as the first full note, but reorganized: author surname-first, and elements separated by periods rather than commas.
Bibliography examples
- Book: Stein, Mara. Quiet Revisions: Editing as a Craft. Bracewell Press, 2019.
- Journal article: Okonkwo, Adaeze C. “Reading between the Citations.” Journal of Humanistic Inquiry 14, no. 2 (2022): 121–44. https://doi.org/10.1234/jhi.2022.047.
- Chapter in an edited book: Choi, Jiwon. “On Voice.” In The Shape of Scholarly Prose, edited by Mara Stein, 88–112. Bracewell Press, 2021.
- Website article: Patel, Riya, and Mahesh Poudyal. “Form and Feeling in Recent Criticism.” Modern Letters Review, March 14, 2022. https://example.org/mlr/12345.
Things to remember about the bibliography
- Alphabetical order by first author surname; secondary sort by title when an author has multiple entries.
- Author surname first in bibliography entries (unlike notes, where the first author appears in natural order).
- Hanging indent on every entry.
- Periods separate the major divisions (rather than commas, which separate elements within a note).
- Headline-style capitalization for both book and article titles, as in Author-Date.
- DOIs as URLs when available, with the https://doi.org/ prefix.
Choosing between the two systems
Three quick rules cover most cases.
If your discipline is social science, business, education, or interdisciplinary work, Author-Date is almost certainly the right pick. The author-year pattern reads quickly inside running prose and lets a reader see who and when at a glance, which matches the priorities of empirical argument.
If your discipline is history, art history, classics, religious studies, philosophy, or musicology, Notes-Bibliography is the convention. The footnote-driven texture matches close engagement with primary sources and lets a writer add asides and supporting evidence without disrupting the main argument.
If your target journal or department has a house preference, follow it. Some journals accept either system; many require one. The author guidelines are the final word.
What RightMyWork does with Chicago
When you pick Chicago Author-Date 18th on the upload screen, the editor applies the Author-Date conventions described above, including parenthetical (Author Year, Page) citations and the year-directly-after-author placement in the reference list.
When you pick Chicago Notes-Bibliography 18th, the editor applies the Notes-Bibliography conventions, including first-full-then-shortened citation patterns in notes, author-inverted bibliography entries, and period-separated bibliography divisions.
Across both, the shared CMOS mechanics apply: American spelling, serial comma, italic on the right elements. Every change lands as a tracked change in Word, so you can accept or reject each one.
Where to go from here
For the rules in their canonical form, the CMOS Q&A and online articles are the best free resource, and the printed Chicago Manual of Style 18th edition is the definitive reference. Both are produced by the people who define the style. If you want a deeper standalone reference on Notes-Bibliography alone, our Chicago Notes-Bibliography 18 guide goes further into the footnote and bibliography mechanics.
When you are ready to apply either Chicago system to your draft, the upload form on the homepage is one click away. Your first 20,000 words are free as a preview (up to 4 documents). Unlock a document for $10, or edit everything on a plan.