Yale Center for Teaching and Learning

Why Are there Different Citation Styles?

Understanding Different Citation Formats

Academic disciplines have varying expectations for how to list citation information. In some instances, even two journals in the same field will use different styles. This guide covers the three main styles used at Yale. All three of these styles require the same basic information, but the order of that information varies, in part because different academic fields emphasize different elements of a source when referring to previous research.

The first two styles are known as “in-text” citation styles, which means that you give some information about the source directly after the quotation, but leave the rest to a list of References (APA) or Works Cited (MLA) at the end of the paper. (1) MLA style, defined by the Modern Language Association, is most common in the humanities. Because humanities research highlights how one piece of writing influences another, MLA style emphasizes the author’s name and the page in the original text you’re using. This information allows scholars to track down easily the exact sentences you’re analyzing. (2) APA style, defined by the American Psychological Association, is most common in the social sciences. Although the author’s name is an important element in APA citations, this style emphasizes the year the source was published, rather than the page number, which allows a reader to see quickly how the research you’re writing about has evolved over time.

The alternative to in-text citation is to use footnotes, which give source information at the bottom of the page. The footnote style we demonstrate here is called Chicago style, defined by the University of Chicago. Chicago style is especially popular in historical research. When developing a historical explanation from multiple primary sources, using footnotes instead of inserting parenthetical information allows the reader to focus on the evidence instead of being distracted by the publication information about that evidence. The footnotes can be consulted if someone wants to track down your source for further research. Chicago style is more flexible than MLA and APA formats, and therefore more complicated to explain. Please see More Notes on Chicago Style Footnotes for more information about how Chicago style is treated in this guide. All three of these styles have different conventions for how to refer to a source in the body of your paper. See Signaling Sources in the Body of Your Paper for more information.

Note: Some works written with MLA or APA style also include what are called discursive footnotes. Rather than giving only the author and title of the sources, these notes discuss in a sentence or two some aspect of the evidence that is not part of the paper’s main argument. Discursive footnotes are also welcome in Chicago style, and many papers that use Chicago style footnotes will mix discursive footnotes with others that just give bibliographical information. See Where to Cite for more information about this kind of footnote.

You should check with your instructors about the style they want you to use. When in doubt, remember that the goal of your citations is to help a reader who wishes to consult your sources directly. Give enough information to make such retrieval easy. The examples below are correct, and can be relied on as guides for citing your sources. But the examples don’t always highlight very slight variations in format among the styles (for instance, whether to use a colon or parentheses to separate the issue number from the volume number in a quarterly journal). For more information about each of these citation styles, see the websites listed below.

Official Sites


Although not officially linked to the authors of MLA, APA, or Chicago style, the following websites are from reputable colleges and offer discussions of the various styles that can supplement the advice in Writing at Yale.


More Notes on Chicago Style Footnotes

In this guide, we use the phrase “Chicago style” to refer to references that take place in footnotes. (The alternative to these notes is “in-text citations”; see Why are there Different Citation Styles? for more information.) But Chicago style is actually very flexible, and offers writers a choice of several different formats. It even invites the mixing of formats, provided that the result is clear and consistent. For instance, the fifteenth edition of The Chicago Manual of Style permits either footnotes or in-text citation styles; it provides information on in-text citation by page number (like MLA style) or by year of publication (like APA style); it even provides variations in footnote style, depending on whether or not the paper includes a full Bibliography at the end.

Because the primary advantages of using footnotes are simplicity and concision, this guide describes only one variation of Chicago style: shortened footnotes in a paper that gives a full Bibliography. What this means is that our examples of Chicago footnotes do not give full bibliographical information at the bottom of the page. Instead, our footnote examples give brief references that would be supplemented, at the end of the paper, with a full Bibliography.

The basic form for a shortened footnote reference is:

footnote number, author’s last name, title of the work, and page number you’ve quoted from.

If the title is more than four words long, you would normally list a shortened version of it.

If your teacher tells you to use Chicago style, or footnotes, you should check to see if the shortened format is acceptable. If you need to give the full citation, the format for each note is nearly identical to MLA format, except that a full footnote generally begins with the first name of the author. If in doubt, we suggest the shortened format (the one we demonstrate here) because it’s the most elegant. It’s also what the Chicago editors recommend.

Note that the footnotes illustrated in this guide focus on publication information, giving only the data necessary for your reader to track down the source. But footnotes can also be used to comment on a source. Such footnotes are often referred to as discursive footnotes, and they are also used in MLA and APA style to add information about a source. Historians, especially, sometimes add brief discussions of a source in the footnote that accompanies its first mention. Ask your teachers for examples of writing that use this technique, or browse through the sample papers posted on other parts of the Writing Center website. See Where to Cite for more information about this kind of footnote.

Chicago Style Bibliographies

For published, print sources, instructions for listing sources in a Chicago Bibliography are the same as for an MLA Works Cited page.

For unpublished or electronic sources, listings in a Chicago Bibliography are slightly different than for an MLA Works Cited. This guide mentions those variations where relevant.