When you write a paper or a book, it's important to include a bibliography. A bibliography tells your reader what sources you've used. It lists all the books, articles, and other references you cited in or used to inform your work. Bibliographies are typically formatted according to one of three styles: American Psychological Association (APA) for scientific papers, Modern Language Association (MLA) for humanities papers, and Chicago Manual of Style (CMS) for the social sciences. Make sure you always check with your superior - whether a professor or boss - about which style they prefer.