Whenever you use information, ideas, or words from someone else's work, you must acknowledge that person. The only exception to this principle is when you use information that is common knowledge, such as the chemical composition of water or the names of the thirteen original states. When you tell readers what sources you have consulted, they can more readily understand your paper as well as the conversation you are participating in by writing it.

How sources are documented varies by field and discipline. Choose a documentation style that is appropriate for the particular course you are taking, and use it properly and consistently. If you are not certain which style to use, ask your instructor.

• MLA: The documentation style developed by the Modern Language Association (MLA) is used by many researchers in the arts and humanities, especially those who write about language and literature.
• APA: Instructors of social science and professional courses in psychology, sociology, political science, communications, education, and business usually prefer a documentation style that emphasizes the author and the year of publication, in part because the style makes it easy to tell if the sources cited are current.
• Chicago: The note and bibliography documentation style presented in The Chicago Manual of Style is used in many disciplines, including history, art, philosophy, business, and communications.
• CSE: The Council of Science Editors (CSE), formerly known as The Council of Biology Editors (CBE), endorses two documentation styles, a name-year style and a number style.
• COS: Columbia Online Style (COS) is designed to supplement already established types of documentation (such as MLA, APA, Chicago, and CBE).