The Modern Language Association, the American Psychological Association and the Chicago Manual of Style have adapted their citation formats for legal document citations from "The Bluebook: A Uniform System of Citation," published by the Harvard Law Review Association. As a legal document, the U.S. Constitution is cited according to the adapted guidelines.
Chicago and APA Styles
According to the guidelines in the "Chicago Manual of Style" (16th ed.) and the APA Style website, Chicago and APA use the same reference format for the U.S. Constitution. First write the name the document, abbreviated "U.S. Const.," and then the article or amendment number. Abbreviate "article" as "art." and "amendment" as "amend." and then write the number. Next, to cite a specific section, add a comma and the symbol "§" before the number. For example: "U.S. Const. art. II, § 1." If the article or amendment has been amended or repealed, add that information in parentheses. For example: "U.S. Const. amend. XVIII (repealed 1933)."
The citation in MLA differs slightly from APA and Chicago. Based on the guidelines in the 7th ed. of the MLA handbook, start the reference with "U.S. Const." Then, write the article or amendment number, preceded by "art." or "amend.," respectively. For the section, use "sec." instead of the symbol "§" and add "Print" or "Web" to show whether you are citing a print or an online source. For example: "U.S. Const. art. II, sec. 1. Web."