A basic APA-style reference includes the last name and first initial of the author, followed by the date of publication, name of article or book in sentence case, name of journal, if applicable, in italics and title-cased, and publication information. When there are two authors for a source, you simply include both last names and first initials split by an ampersand. For example, a journal citation with two authors would look something like this: Brown, A. & Collins, D. (1994). The monthly study. Science Review, 5, 12-14.
Three to Seven Authors
When a source has three to seven authors, you continue to list all of their last names and first initials, separating each with a comma. The last author is preceded by an ampersand. For example, a book citation would look like this: Brown, A., Collins, D., Cooper, S., & Nolan, B. (2011). The long road. New York, NY: Pear Publications.
More than Seven Authors
References should list no more than seven authors. For sources that have more than seven authors, the first six authors are listed by last name and first initial separated by commas. An ellipsis is used after the sixth author in place of the other authors' names and then the last author is listed. As an example, a book reference would look like this: Pan, P., Brook, A., Sam, L., Brown, M., Brody, A., Chan, M., ... Woods, A. (2002). Knowing the difference. Boston, MA: Basic Publications.
Often sources will have an organization, association or other type of group listed as the author. In these cases, the group should be listed in place of the author when including the source in an APA-formatted reference page. Here is an example of a book reference written by an association: American Math Association. (2004). Geometry in middle school. Long Beach, CA: Periodical Publications.