When using APA to format a paper, knowing when you must cite information can be difficult. Each time information is derived from a source it must be noted, even if the same source is used multiple times. Depending upon the source, subsequent citations may differ from the first.
One or Two Authors
If a source has one author, all citations are done one of two ways. The last name of the author can be mentioned in the text with the publication year in parentheses, such as "Doe (2010) found that ... ." With two authors, both names are listed: "Smith and Jones (2013) ... ." With the second option, the author's last name, a comma and the year are placed within parentheses after the pertinent information. If there are two authors, the names are separated by an ampersand, such as (Smith & Jones, 2013).
Three to Five Authors
The first time a citation occurs, all the authors' last names are listed. Within the text, the publication year is included within parentheses, such as "Alpha, Bravo, Charlie, Delta, and Echo (2001) determined that ... ." Alternately, the names are within parentheses, separated by commas, except for the last one, where an ampersand is used. A comma is followed by the year. All subsequent citations include just the first author's name followed by "et al" (for "et alia," or "and others"), a comma and the year.
If a source has six or more authors, the same formats are used for all citations. The first author's name is listed within text followed by "et al." The publication year is placed inside parentheses. A variation places that same author information, a comma and the year inside parentheses.