APA style was developed by the American Psychological Association. The social sciences often use APA style for documenting sources.
Publication Manual of the American Psychological Association (7th ed.) by MLA was developed by the Modern Language Association. The humanities typically use MLA format to cite sources.
MLA Handbook (9th ed.) by Turabian style is named for its developer Kate Turabian, and is used in various disciplines, including history. This style is sometimes referred to as Chicago style since it is based on The Chicago Manual of Style.
A Manual for Writers of Research Papers, Theses, and Dissertations (9th ed.) by 
The Chicago Manual of Style (17th ed.) by 
Student's Guide to Writing College Papers, Fifth Edition by 