Citation styles differ mostly in the location, order, and syntax of information about references. The number and diversity of citation styles reflect different priorities with respect to concision, readability, dates, authors, publications, and, of course, style.
There are also two major divisions within most citation styles: documentary-note style and parenthetical style. Documentary-note style is the standard form of documenting sources. It involves using either footnotes or endnotes, so that information about your sources is readily available to your readers but does not interfere with their reading of your work.
Professor Scott asserts that “environmental reform in Alaska in the 1970s accelerated rapidly as a pipeline expansion.”: (Scott 1999,23)
This is generally considered an abbreviated form of citation, and it does not require footnotes or endnotes, although it does require the equivalent of a "Works Cited" page at the end of the paper. It is easier to write, but might interfere with how smoothly your work reads.
With so many different citation styles, how do you know which one is right for your paper? First, we strongly recommend asking your instructor. There are several factors which go into determining the appropriate citation style, including discipline (priorities in an English class might differ from those of a Psychology class, for example), academic expectations (papers intended for publication might be subject to different standards than mid-term papers), the research aims of an assignment, and the individual preference of your instructor.
If you are a teacher or instructor, you may also wish to distribute examples of plagiarism and legitimate citation, and then go over the differences together with your classes. This will clarify some of the common misconceptions about plagiarism and reduce the likelihood of "honest mistakes," while at the same time showing how serious you are about the issue.
If you want to learn more about using a particular citation style, we have provided links to more specific resources below.
MLA (Modern Language Association)
ACS (American Chemical Society)
IEEE (Institute of Electrical and Electronics Engineers)
NLM (National Library of Medicine)
Vancouver (Biological Sciences)
AAA (American Anthropological Association)
[Note: the AAA style is based on the Chicago style, so for specific questions not addressed in any of the AAA style guides, please use the links above or consult The Chicago Manual of Style (14th edition, 1993)]
APA (American Psychological Association)
APSA (American Political Science Association)
Any time you quote, paraphrase, summarize, or reference a source, you must cite that source in a parenthetical note or a footnote and append a bibliography, which, depending on the discipline, may be called “Works Cited” or “References.”
All citations share some basic components, including the title of the work being referred to, the name of the work’s author(s), the publisher, and the date of publication. Beyond these general requirements, styles of citation vary by discipline and by professor’s preference. In the humanities, the most commonly accepted citation style is that of the Modern Language Association (MLA). In the social sciences, the American Psychological Association (APA) style is widely used. Historians typically employ the footnote style described in The Chicago Manual of Style (CMS). Each scientific discipline has its own protocols and formats, usually available in a style manual produced by the discipline’s scholarly organization. You’ll see that many academic disciplines encourage the use of in-text parenthetical citations rather than footnotes.
Once you join a department as a concentrator and begin your junior year work, the department should provide you with information about expected citation formats and practices in the discipline. Often, individual professors will provide you with information about their preferred citation format.
The examples that follow employ four different citation styles. For the specifics of each style, you should consult an official style manual, because the rules for citation vary greatly for different kinds of sources. For example, books are cited differently from articles, which are cited differently from e-mail correspondence. You’ll need to consult a style manual to determine the proper format for each source type. (A list of recommended style manuals may be found at the end of this section.)
Example 1: Literary Studies (MLA).
The MLA requires a parenthetical citation in the body of the text that corresponds to an entry in the Works Cited at the end. A citation for a quotation from a book in the MLA style is formatted this way:
As Frank Lentricchia argues, The Waste Land should not be understood as a logical sequence of events but as “an intellectual and emotional complex grasped in an instant of time” (194).
The parenthetical citation “(194)” refers to a page number from a book by Frank Lentricchia. Publication information about the book would be found in the Works Cited, where it would be formatted this way:
Lentricchia, Frank. Modernist Quartet. New York: Cambridge University Press, 1994.
Example 2: Psychology (APA).
The APA also requires parenthetical citations in the body of the text, though these citations typically include the author and the date. A citation for a summary of an article in the APA style is formatted this way:
Studies that examine links between cardiovascular and mental activity must understand that cardiovascular activity itself comprises a suite of variables (Van Roon, Mulder, Althaus, and Mulder, 2004).
The parenthetical citation “(Van Roon, Mulder, Althaus, and Mulder, 2004)” refers to an article by the four listed coauthors. Publication information about the article would be found in the References, where it would be formatted this way:
Van Roon, A., Mulder, L., Althaus, M., and Mulder, G. (2004). Introducing a baroflex model for studying cardiovascular effects of mental workload. Psychophysiology, 41, 961–981.
Example 3: History (CMS).
CMS, or “Chicago,” is a style in which citations are presented in footnotes. A citation for a quotation from an article in the Chicago style is formatted this way:
Nineteenth-century bohemians were more dependent on mainstream culture than might at first appear. As one scholar puts it, “Bohemia”s self-designated types always existed in symbiotic relation to bourgeois culture rather than in opposition to it.”1
The footnote “1” would refer to a note at the bottom of the page containing full publication information and formatted this way:
1. Christine Stansell, American Moderns: Bohemian New York and the Creation of a New Century (New York: Henry Holt and Co., 2000), 18.
Example 4: Biology.
Citation styles in math, science, and engineering tend to vary from journal to journal. Following a quotation or a reference to the text, the author might name the source, or might use a superscript number such as 1 or a parenthetical number such as (1), to indicate the number of the article in the final list of references. The journal Nature Genetics uses the following format for articles, and the references are listed numerically rather than alphabetically:
13. Herron, B. J. et al. Efficient generation and mapping of recessive developmental mutations using ENU mutagenesis. Nat. Genet. 30, 185–189 (2002).
Because of the variety of citation styles for math, science, and engineering, you should consult your professor about their preferences and expectations.
An electronic source is any source that exists primarily in electronic form and is accessed primarily through electronic means. Websites, online periodicals, online books, e-mails and postings, and even CD-ROMs are all forms of electronic sources. But be careful: not all materials found through electronic means are necessarily electronic sources. For example, if a PDF of an article you found through a database on the library’s website was originally published in a printed journal, then the article doesn’t qualify as an electronic source. In short, there’s a difference between electronic sources and sources that are accessed electronically.
When citing an online source, your citation should contain the following elements:
- the author or editor (if available),
- the title of the text (if different from the name of the website),
- the name of the website,
- the name of the site’s sponsor or associated institution or organization,
- the date you accessed the site,
- the electronic address (URL).
For example, a short work posted on a website would be formatted in MLA style as follows:
McCort, Dennis. “Kafka and the Coincidence of Opposites.” Romantic Circles Praxis Series: Romanticism and Buddhism. February 2007. Romantic Circles. 21 April 2008. ≺ http://www.rc.umd.edu/praxis/buddhism/mccort/mccort.html ≻
This citation includes not only the author’s name and the work’s title, but also other important information, including the date of the work’s publication on the site (February 2007) and the date the website was accessed (21 April 2008).
The published guides of the MLA, APA, and Chicago styles include detailed descriptions of how to cite most electronic sources. As explained earlier on this website, the emerging nature of this new technology means that conventions are forming quickly, and the variations among citation styles vary considerably. Be sure to look up the appropriate form of citation and to consult your professor about any points of confusion.
Recommended Style Manuals
For complete coverage of MLA, APA, and Chicago citation styles, you should obtain the most recent edition of each style’s official manual: MLA Handbook for Writers of Research Papers (8th edition, 2016), the Publication Manual of the American Psychological Association (6th edition, 2009), and The Chicago Manual of Style (16th edition, 2010). For an online guide to these styles, visit the Library website, at library.princeton.edu/help/citing-sources. A good commercially published guide is A Pocket Style Manual, by Diana Hacker and Nancy Sommers (2014), which includes brief but substantial overviews of the MLA, APA, and Chicago styles.