APA and MLA are two common formatting styles used for research papers. APA (American Psychological Association) is typically used in the social sciences, while MLA (Modern Language Association) is typically used in the humanities. The main difference between the two styles is in the way in-text citations and references are formatted. APA uses parenthetical citations with the author's name and date of publication, while MLA uses parenthetical citations with the author's name and page number.