Citation acknowledges any source that has directly influenced your language, ideas, or arguments. You should cite not only what you quote, but also what you paraphrase. Putting an idea or argument into your own words may modify it, but does not make you the sole author.
In addition to giving due credit, citation allows your readers to locate your sources. Most formal writing is a dialogue with others who have addressed the same topic, and your reader needs to know who they are and where, exactly, you have encountered their ideas.
Also, if you don't cite, you'll be guilty of plagiarism and punished.
The three most commonly used at by OPRFHS teachers are APA, MLA, and Chicago.
Created by the American Psychological Association, this style is commonly used in the social sciences. It uses in-text or parenthetical citations.
Created by the Modern Language Association, this style is commonly used in the humanities. It uses in-text or parenthetical citations.
Created by the University of Chicago Press, this style uses a "notes and bibliography" style where superscript numbers in the text refer to either footnotes or endnotes with complete citation infromation on the first citation. Historicans love to use footnotes or endnotes.