APA citation style is most frequently used in the social and behavioral sciences, e.g. psychology, linguistics, education, as well as nursing and business.
The first style rules were published in 1929. The American Psychological Association has produced 7 editions of the Publication Manual in the ensuing 80+ years.
APA style relies on in text citations (author, date) for paraphrased, summarized, or quoted material within a paper. In text citations correspond to sources in the References list at the end of the paper.