It is an academic writing style and format that was invented by the American Psychological Association. It is commonly used in social sciences. In general, an essay should have the title page, double-spaced, with 1″ margin on all sides. It should also have the words “running head:” as the header of the title paper followed by the title of the paper in CAPS. The APA style uses an author-date citation system with a reference list on the last page. Here is a sample APA style essay.