The Publication Manual of the American Psychological Association, 7th ed. (2020) is the authority used by writers in the social sciences and some natural sciences.
Unofficial: CSUF APA Style Quick Reference Guide (PDF) provides a two-page overview of some of the most common citation needs for both the references list and in-text citation.
Official: APA Style Help offers support resources from the APA, including Style and Grammar Guidelines (which provides information on in-text citations and references, among other important topics) and Instructional Aids (which provides links to tutorials and webinars, handouts and guides, and sample papers).
For the most comprehensive coverage of APA style, including citation rules, please remember to consult the print APA publication manual. A copy is kept at the Research Center (first floor of Pollak Library North) for in-library use.
Also Available Online:
OWL (Online Writing Lab) at Purdue University. Purdue University's OWL is an excellent source to use for any citation style, including APA.