Overview of Citing Sources
Citing sources in the text, no matter the documentation style, allows the reader to refer quickly and easily to the list of sources and see the full information about the source. Each citation should be "keyed" directly to an entry on the list of sources so that the reader can see immediately which source the citation is referring to. It should take no more than a few seconds for the reader to notice a citation, flip to the list of sources, and see which source matches.
The citation itself has only a small amount of information so that it does not impede readability. If the citations had too much information, the essay would be hard to read. Citations should be kept as short as possible because the full information is at the back of the essay. For example, if you use the author's name in the sentence, do not include it in the citation. Also to maintain readability, place citations at the end of a sentence or at a place in the sentence where there is a pause, such as just before a comma, unless you have more than one citation in a sentence.
In MLA format, an in-text citation might look like (Zinsser 14). That indicates the writer took the quotation or paraphrase from page 14 of a work by Zinsser. When the reader sees this citation, he or she should be able to flip to the Works Cited page, run a finger down the left-hand side, and find the name Zinsser in alphabetical order. That entry will give the remaining publication information, such as the title and date of publication. In APA, the citation will look like (Zinsser, 1998, p. 14), but the process works the same. Footnotes in Chicago will also match up quickly to entries on the Bibliography. The citation should always match the item at the left-hand side of the list. The reader should not have to read within the list looking for the matching entry.
When a source has an author (either a person or an organization), making sure the citation and entry on the source list match is easy. However, even when a source has no author, that match must still be clear. For sources with no author or corporate author, in MLA and APA, the title will be the first element of the entry on the source list. Therefore, use the complete title, if it is brief, or the first important word or words of the title in the citation. For example, take an essay that uses an anonymous editorial titled "When Don't Smoke Means Do" from the New York Times website. In MLA style, the citation could be ("When Don't Smoke") because that is a shortened version of the title. In APA, the citation could be ("When Don't Smoke," 2006). Notice the quotation marks, which indicate that the words "When Don't Smoke" is part of a title. Because the source is online, it has no page numbers. In Chicago, this source would be listed by the periodical title, New York Times, so that title would appear first in the footnote.
Ultimately, every source you cite in the essay should have a matching entry on the list of sources, and every source on that list must be cited in the essay. There should be no extra sources in either place.
In MLA and APA styles, there are only two possibilities for correct in-text citations: the last name of the author(s) or the title (shortened if necessary) if there is no author. Each of these would be succeeded by the page number if the source includes page numbers.
To learn about citing sources more specifically in MLA, APA, or Chicago style, see the relevant pages for those styles.