What Is a Citation? Definition, Styles, and Examples

APA, MLA, Chicago, and Electronic Citation Styles

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In any research paper, you draw on the work of other researchers and writers, and you must document their contributions by citing your sources, say Diana Hacker and Nancy Sommers in "A Pocket Style Manual, Eighth Edition." Citations, then, are the means by which you credit other researchers and writers when you use their work in your papers. Understanding how to cite sources can be tricky, particularly since there are different styles for writing papers, including American Psychological Association, Modern Language Association, and Chicago styles.

Electronic sources also come with their own specific citation rules in each of these styles. It's important to learn proper citation styles to avoid plagiarism in your research papers.

APA Citations

American Psychological Association (APA) style is often used in social sciences and other disciplines. With APA or any of the styles listed in this paper, you need to use a citation if you quote text from another source, paraphrase an author or authors' ideas, or refer to her work, such as a study, original thinking, or even an elegant turn of phrase. When you cite a source, you can't simply repeat most of the words from the work to which you are referring. You have to put the ideas into your own words, or you need to quote the text directly.

There are two parts to citations for APA and other styles: the short-form in line, which directs readers to a full entry at the end of a chapter or book. An in-line citation differs from a footnote, which is a note placed at the bottom of a page.

An in-line citation—also called the in-text citation—is placed within a line of text. To create an in-line citation, cite the name of the author and the date (in parentheses) of the article, report, book, or study, as this example from "A Pocket Style Manual" shows:

Cubuku (2012) argued that for a student-centered approach to work, students must maintain "ownership for thier goals and activities" (p. 64).

Note how you list the page number at the end of the in-text citation in parentheses followed by a period (if it is at the end of a sentence). If there are two authors, list the last name of each, as in:

"According to Donitsa-Schmidt and Zurzovsky (2014), ..."

If there are more than two authors, list the last name of the first author followed by the words "et al.," as in:

Herman et al. (2012) tracked 42 students over a three-year period (p. 49).

At the end of your paper, attach one or more pages titled "References." That section is essentially your biography. Readers of your paper can then turn to the references listing to read the full citations for each of the works you cited. There are actually many variations for references citations depending, for example, on whether you are citing a book, journal article, or newspaper story, or the many different kinds of media, including audio recordings and film.

the most common citation is to books. For such a citation, list the last name of the author, followed by a comma, followed by the first initial(s) of the author(s), followed by a period. You would put the year the book was published in parentheses followed by a period, then the title of the book in italics using sentence case, followed by a comma, the place of publication, followed by a colon, and then the publisher, followed by a period.

"A Pocket Style Manual" gives this example:

Rosenberg, T. (2011). Join the club: How peer pressure can transform  the world. New York, NY: Norton.​

Though the citations here won't print this way, use a hanging indent for the second and any subsequent lines in each citation. In a hanging indent in APA style, you indent every line after the first.

MLA Citations

MLA style is often used in English and other humanities papers. MLA follows the author-page style for in-text citations, notes Purdue OWL, an excellent citation, grammar, and writing website operated by Purdue University. Purdue gives this example of an in-text citation, which is also called parenthetical citation in MLA style. Note that in MLA style, page numbers don’t typically appear unless the sentence or passage is a direct quote from the original, as is the case here:

Romantic poetry is characterized by the "spontaneous overflow of powerful feelings" (Wordsworth 263).

At the end of the paper, attach a "Works Cited" page or pages, which is equivalent to the "References" section in APA style. "Works Cited" section citations are very similar in MLA and APA style, as in this example of a work with multiple authors from Purdue OWL:

Warner, Ralph, et al. How to Buy a House in California. Edited by Alayna Schroeder, 12th ed., Nolo, 2009.

Note that you would also use a hanging indent in MLA, but it tends to be a bit shorter; move the second and subsequent lines in by three spaces. Spell out the first name of the author(s) in MLA style; add a comma before "et al."; use title case for the book, journal, or article title; omit the place of publication information; follow the name of the publisher with a comma; and list the date of publication at the end.

Chicago Style Citations

Chicago is the oldest of the three major writing and citation styles in the United States, having begun with the 1906 publication of the first Chicago style guide. For in-text citations, Chicago style, which comes from the "Chicago Manual of Style" from the University of Chicago Press, is pretty simple: the author's last name, date of publication, a comma, and page numbers, all in parentheses, as follows:

(Murav 2011, 219-220)

At the end of the paper, insert a list of references, which in Chicago style is called a bibliography. Books, journals, and other articles are cited in a manner similar to APA and MLA style.

List the author's last name, a comma, and the full first name, followed by the title of the book in italics and title case, the place of publication, followed by a colon, followed by the publisher's name, a comma, and the date of publication, all in parentheses, followed by a comma and the page numbers.

Kate L. Turabian, in "A Manual for Writers" (a student-geared version of Chicago style), gives the following example:

Gladwell, Malcolm, The Tipping Point: How Little Things Can Make a Big Difference (Boston: Little Brown, 2000), 64-65.

You also use a hanging indent in the bibliography section of a Chicago style paper, with the indent moved in three spaces. For article or journal titles, list the title in regular (not italic) type encased in quotation marks.

Electronic Sources

Electronic source citations are similar to citations of published works except for two issues: You need to include the URL of the source, and a large percentage of online sources may not list an author. 

In APA style, for example, list an online source in the same way you would cite a book or article, except that you need to include the type of information you are accessing (in parentheses), as well as the URL. If the online source lacks a listed author, start with the name of the group or agency providing the information. "A Pocket Manual of Style" provides the following example of an APA electronic source citation:

U.S. Department of Agriculture, Economic Research Service. (2011). Daily intake of nutrients by food source: 2005-08. ​[Data set]. Retrieved from http:www.ers.usda.gov/data-products/food-consumption-and-nutrient-intakes.aspx.

As with other citations, use a hanging indent for the second, third, and fourth lines of this source. For Chicago style, use the same method as described previously but add the URL, as in this example:

Brown, David. "New Burden of Disease Study Shows World's People Living Longer but with More Disability," Washington Post, December 12, 2012. http://www.washingtonpost.com/.

Note that Chicago style includes only the home-page URL and not the full URL; that can change, however, from one regime to the next.

MLA style used to require you to list the date you accessed the information, but that's no longer the case. To cite an electronic source, use the same style as discussed previously, but replace the period after the date with a comma and then list the URL.