Chicago Style Basics: Notes-Bibliography and Author-Date

Two systems under one name

Chicago style, published by the University of Chicago Press, is not a single citation format. It offers two documentation systems, and choosing the right one is the first step. The notes-bibliography system uses footnotes or endnotes, marked by a superscript number in the text, together with a bibliography at the end. It is common in history, art history, religion, and many other humanities fields. The author-date system looks more like APA: a short parenthetical citation with author and year appears in the text, and a reference list carries the full details. It is more common in the sciences and social sciences.

This guide describes general ideas and assumes the seventeenth edition, which is the version many courses use. A newer edition may exist, and instructors sometimes name a specific one. Check the current manual or your instructor's instructions before you commit. If you are not told which system to use, ask, because a paper cannot mix them.

How notes-bibliography works

In this system, a superscript number appears at the end of a sentence or clause that draws on a source. A matching note, placed at the foot of the page or collected at the end of the paper, provides the citation. The first note for a source usually gives full details: author name in normal order, title, publication information, and page number. Later notes for the same source are shortened, often to author surname, a short title, and a page number. Some instructors permit a shortened form even for first citations when a bibliography is included, so confirm what is expected.

The bibliography lists the sources at the end of the paper, alphabetized by author surname, with a hanging indent. Entries invert the first author name and separate elements with periods rather than the commas common in notes. A generic pattern for a note is First Name Surname, Title of Work (Place of Publication: Publisher, Year), page. A generic bibliography entry is Surname, First Name. Title of Work. Place of Publication: Publisher, Year. The differences in punctuation between notes and bibliography matter, so check both patterns in the manual.

Notes can also hold brief commentary, though many instructors prefer that long digressions stay out of the footnotes. Keep notes concise and relevant.

How author-date works

The author-date system places a parenthetical citation right in the sentence, typically the author surname and year, with a page number after a comma or colon when you point to a specific passage. The reference list at the end gives the full entry, with the year placed immediately after the author name. This makes it easy to see how current a source is, which is why science and social science fields often favor it.

A reference entry in this system is similar in spirit to its bibliography counterpart in the other system, but the year moves forward. A generic pattern reads Surname, First Name. Year. Title of Work. Place of Publication: Publisher. Some details of punctuation and capitalization differ from APA even though the structure looks similar, so do not assume the two are interchangeable.

When several works by one author share a year, letters are attached to the year, such as 2020a and 2020b, so that readers can tell them apart in text. As always, make sure that every in-text citation can be matched to a list entry and vice versa.

Shared conventions and special cases

Both systems follow certain habits. Titles of standalone works are italicized, while titles of parts, such as articles and chapters, appear in quotation marks. Headline-style capitalization is generally used for titles. Authors of edited works, translators, and editors have specific ways of being credited, and the manual explains where their names go. If your source has several authors, there are rules about how many to name in notes versus in the bibliography; verify the current limits instead of relying on memory.

Chicago has long recognized that sources like websites, social media posts, and personal communications may not belong in a formal bibliography. In many cases they can be handled in a note or in text only. Whether to add them to a bibliography is a judgment call that may depend on your instructor, so ask.

The abbreviation ibid., once used heavily for repeated notes, is now discouraged in many contexts in favor of shortened notes. If your instructor still accepts it, follow their lead.

Choosing and applying a system

Start by reading your assignment or journal guidelines. If they name a system, use it. If you have a choice, think about your discipline's habits and your readers' needs. Notes-bibliography suits writing that engages closely with primary sources and allows commentary in the notes. Author-date suits writing that references many sources briefly and benefits from seeing years at a glance.

Once you have picked one, collect the same information for every source: author, title, container if any, publisher, place of publication when needed, date, page range, and a link or identifier for online items. A citation generator can format these fields to match either system, but check the output against the manual, especially for punctuation and the choice between full and shortened notes.

Finally, keep your notes and your bibliography or reference list consistent. If a source appears in a note but is missing from the bibliography, or the reverse, readers will notice. Careful proofreading is the best defense.

A last practical point concerns tools. Word processors can insert footnotes and renumber them automatically, which prevents the numbering slips that are easy to make by hand. Let the software handle numbering, and spend your own attention on the content of each note: is the source identified clearly, is the page number accurate, and does the shortened form still point unambiguously to one entry in your bibliography? Those three questions catch most of the errors a reader will care about. If your department supplies a template or sample paper, compare your notes with it before submitting, because local examples often reveal the preferences of the person who will mark your work.

Frequently asked questions