Letters patent (pl. letters patent) are so named from the Latin verb pateo, to lie open, exposed, accessible,  being called in full letterae patentes. They are a type of legal instrument in the form of an open letter issued by a monarch or government, granting an office, right, monopoly, title, or status to a person or to some entity such as a corporation. They are thus a form of open or public proclamation. The opposite of letters patent are letters close (Latin: litterae clausae), which are personal in nature and sealed so that only the recipient can read their contents. Letters patent can be used for the creation of corporations or government offices, or for the granting of city status or a coats of arms. A particular form of letters patent has evolved into the modern patent granting exclusive rights in an invention.
In the United Kingdom and countries formerly under that country's influence, letters patent are issued under the prerogative powers of the head of state ("royal prerogative"). They constitute a rare, if significant, form of legislation without the consent of the parliament. Letters patent may also be used to grant assent to legislation.
In the United States, the forgery of letters patent granted by the President is a crime subject to fine and/or imprisonment up to ten years (18 U.S.C. § 497). Without letters patent, a person is unable to assume an appointed office. Such an issue prompted the Marbury v. Madison suit, where William Marbury and three others petitioned the United States Supreme Court to order James Madison to deliver their letters for appointments made under the previous administration.